installation

Why are you installing beta version?
Ubuntu 8.10 have a stable version:

http://ubuntu.hugi.is/releases/intrepid/ubuntu-8.10-desktop-i386.iso

Hi :)

The best plan for all linux distros is to try booting up from the Cd and see what it looks like without installing anything. There might be some problems worth asking in the relevant forums about but even issues that seem quite huge can be quite trivial to fix, with help. Of course sometimes a minor issue can turn out to be a problem so it's worth asking a separate question about each issue you have trouble with, before installing. For Ubuntu download from here ...
http://www.ubuntulinux.org/getubuntu/download
32bit desktop 8.04 (or 8.10) is almost always the best choice. Make a Cd, usually i find really cheap Cd that are 'write once' are better than more expensive types and i tend to get a pack of 10 or something. Just double-clicking the iso image is usually enough but here's a guide in case it's not so easy
https://help.ubuntu.com/community/BurningIsoHowto
and then booting up from the Cd is normally easy, just put the Cd in the drive and shutdown and restart the computer, again another guide in case of trouble with that
https://help.ubuntu.com/community/BootFromCD
This should get you to a menu with an option to "Try Ubuntu without installing anything". This is well worth trying, as i said above. If you like it then the best way to install is to shrink your Windows down by at least about 10Gb and install Ubuntu alongside so that you can keep booting up into Windows when you need to get something done quickly but can use and explore Ubuntu at you own pace. Most of us keep a working Windows around somewhere. It's best to avoid installing within Windows using the Wubi as it just makes things difficult later and is a bit like buiding a house on shifting sands. This guide shows how to make a proper dual-boot that makes your system much more robust and flexible than either OS on it's own ...
https://help.ubuntu.com/community/WindowsDualBoot

Hope i haven't put you off! Good luck and welcome to linux
Regards from
Tom :)