can I copy my ubuntu installation from external hard disk to my laptop fixed hard disk

Yes and no.
So first of all, are you saying you had ubuntu installed on a single NTFS partition? Are you sure? I didn't know that's possible.
Secondly, I have an own experience of making backups on an external HD of exactly the same size by cloning the internal HD - and then just copying files. There were minor issues, since the GRUB confic and my fstab contained something that's a unique ID of the HD and the partitions, rather than just its location like /dev/sda1. So at least you will nee to fix your grub config (or the config at boot time) and the fstab by hand. Also, if the internal HD is differently partitioned you will need to fix your fstab. Theoretically it should work then (supposed you have grub installed on your HD) - just partition the main HD accordingly and copy all the files (I use rsync -auv) but it's obviously something very "experimental".
If the ext. HD is a laptop HD, you could also just pop it in your laptop (and again fix the fstab and grub config). That's somewhat less ecperimental.

However, if you don't have much experience with linux yet (as in you're not comfortable with editing your configuration files by hand etc.) then I'd rather do a fresh install, and then copy your files over.

Also make sure you backup all your important files before doing anything.

Sameer,

from what I can see/understand you have ubuntu installed under windows ? if that's the case then you have the distribution called wubi; pls correct me if I'm wrong.

if that is the case and you decided that would like to have ubuntu only, then I would suggest to go for the full ubuntu standalone install (not dependent on win). in order to do that pls download the image .iso file from the net, burn a CD and install it to your internal HD.

but before doing that pls save to some other media or to a different data only partition all data that you care about be it in win or ubuntu. if saved to a different media then before installing ubuntu create a data only partition and transfer saved data to it. then install ubuntu to the free space left on the HD. ubuntu can be installed and be booted on primary as well as volumes on extended partitions.

hope this helps.
peter b

 Thanks Peter B
You are absolutely correct.
I have been using wubi.
Now please clarify the saving of files to some other media.
Can i use the same external drive to back up all the data on a different
partition.
Further is there a way to save my current settings of ubuntu that I can
apply to the fresh installed OS on my internal HD.
Thanks a lot for helping me
Sameer

In principle, saving all data on the external HD should be fine, provided you obviously dont connect it during the installation to the laptop. The safest thing however, in general, is to have two backups, on different media (one of mine is locked in a fireproof safe) - the average lifetime of a laptop HD is just over 3 years, so they do fry somtimes, and things can go wrong during backup (happened both to me...).

To keep your settings, what I'd try is to install two users on your newly installed system. One with your old user name and one with a new user name (just as a safety backup).
After installing, you log into a text shell (check out the options on the login screen), s.t. you don't actually use any of your gnome/kde config files, and can copy _all_ contents of your old home directory to your new one. Like "cp -af /[your old home directory, whereever it is mounted on the system]/* /home/[your user name]/". Then, you go to your favourite church/synagogue/mosque, pray, and log out of the text shell and log in graphically - hopefully it should work. Has always worked for me, but there may be a few settings that get lost, e.g. if the new version of some program is a higher one than the old version.

Sameer,

you can use the external HD to save your existing data to a data partition - there's nothing wrong with it provided that it is NOT the same partition that contains the current win/ubuntu installation which you'll probably, after the new ubuntu standalone is installed, delete and use its space in the future as additional storage space.

re saving to some other media, sure you can do that too as an additional safety measure; you can use CD/DVD's either R or RW or usb pendrives that nowadays are available at v low prices and large capacity; you can use also expresscards connected to either the pc expresscard interface if available or to usb ports with proper adapters.

re wubi system settings and configuration and eventual transfer to the new ubuntu install - to be absolutely honest, I am quite unfamiliar with wubi, never used it, but my gut feeling tells me that such an exercise would be like a shot in the dark with many more misses than hits for many reasons last but not least the fact that linux is installed using an existing os which is totally different than linux standalone install; win is notorious of being v weak in security, prone to all kinds of viruses and attacks with strange and unpredictable behaviour etc. just look at the latest conficker saga; wubi is installed the way I see it as a client under the host win, to me that is something that I do not want to have on my pc; give linux/ubuntu the autonomy it deserves.

however, there may be users that accomplished such a task successfully - you may try finding solutions on wubi's forums or support sites. personally, I would suggest just forget about wubi settings and their transfer to the full ubuntu standalone - the time required to set up and customize the new install the way you want it is peanuts compared to the problems you might run into by going the path of wubi settings transfer to the new install.

as far as ubuntu distro to use for the new install, I'd recommend 804 hardy gnome distribution, it is Long Term Support distribution unti 2011, it is solid and v stable and wifi proved to not be a problem at all if not supported right out of the box. I had very good experience and results with 810 intrepid, it has better support for wifi out of the box but is supported for another year only.

so, that's my 2 cents worth of how to go about setting the pc the new way you described. it's your call.

regards,
peter b