Downloading Ubuntu onto an 11 year old HP Compaq laptop with an external monitor and external broadband antenna

I need advise.
My Toshiba Satellite developed a hard drive problem and died on me. I have replaced it with an 11 year old HP Compaq Presario V5000 with a broken monitor to which I attached an old external monitor.
I get my internet from a kind neighbor using an external broadband antenna(Rosewill RNX-N180UBE).

Unfortunately after many years of use I only have 2.97 Gigs of hard drive memory left on the HP.

Normally I would just download the disc that came with the computer and start fresh, but as you might imagine after 11 years, that is long gone.

I had Ubuntu loaded on my Toshiba using a partition so I have some experience with it, but only as part of a dual operating system.

The current set-up I have is slow and prone to freezing and I was hoping that if I replace the Windows XP operating system I have with Ubuntu that it would resolve my problems with lack of hard drive memory as well as some of the difficulties I am having with the computer's operating.

Please understand I am not expecting miracles. My concern is that the monitor I am using is not a widescreen and the laptop is. I was able to re-configure using XP, but am concerned that I may not be able to with Ubuntu.

Understand, if I replace the XP with Ubuntu, there is no going back for me as I have no recovery disk.

I am disabled and having a computer is my only access to the outside world.
I don't even own a TV because I prefer watching television on the computer.
I need some reassurance that if I switch over to Ubuntu that I will still have a working computer.
My Toshiba only lasted 14 months before it died on me and it was just pure good luck that I managed to even get this jury rigged system up and running.
It's not worth the cost of replacing the hard drive since my funds are limited, instead I decided to start saving up simply get a used laptop.
I figure it will take about a year to do that and in the mean time I need to maximize the system I have.
The Presario has a 40 Gig hard drive and 512 Megs of RAM.
Any advice anyone can get would be appreciated.
Forgive the length of this, but I am more than a little stressed.
The computer tends to freeze up a lot and honestly I don't know if it's the computer or the software, but I need to do something to improve my situation before I take a baseball bat to the whole thing.

So, what do you think? Will downloading help?

And can it re-configure from the widescreen format on the laptop to fit on monitor I have.
I realize it is kind of an odd situation, but I am pretty desperate.
No way I can go an entire year without a computer and I am at my wits end dealing with the constant freeze ups on the XP.

 Again, I realize I can't expect miracles, but do you think it is worth the risk?

Right now I have a system that works somewhat.
Dom I take the risk switching over to Ubuntu and lose even that, or do you think the risk is minimal enough to try.

Again, apologizes for the length of this.

Any further information you need please let me know and I thank you in advance.