Well, don't give up on Ubuntu yet!
Are you at all familiar with checking md5's? It's a fairly simple process but completely unfamiliar to lots of Windows users.
There are many md5 utilities available that run in Windows. What an md5 utility does is run a file (such as the Ubuntu download) trhu some sort of algorithm that produces a long alpha-numeric md5 checksum when it's done. You compare the resulting checksum (also called a "hash") against a checksum supplied by the originator of the file to see if your download was received correctly.
Go back to the website where you downloaded your .iso. On that page somewhere there should be a list of MD5's. Help me out here...where did you go, and what did you download? On the Ubuntu download pages, the MD5 sums are just below the download links.
Checking the download md5 is easy, because it's just one big file so there's only one md5. After you've converted the .iso to a bootable CD there are hundreds of files to check. And I don't know of any place on the website that supplies the proper md5's for all those files. That's why on the "Start or Install" splash page there's an option to "Check CD for Errors". If you run that, and the CD comes back with any errors whatsoever, there's no point in proceeding any further with the install. The CD is flawed. It has to be perfect.
So, here's what I'd suggest. Do you still have the download saved on your HDD? Download an easy Windows md5 utility, like
md5Summer, and run it across your download. Write down the resulting checksum or save it to your desktop. Find the website you used, find the MD5's, and check it against the md5 you got from md5Summer. If they don't match, your download was bad and you must try again. If they do match, then your burn went bad. Try it again, use good quality media, burn it at 2X, and don't do anything with the PC while it's burning. Walk away and get a cup of coffee. Oh, before you do that, check your Power Mgmt and make sure to set it to "Always On". You don't want the PC to hibernate in the middle of the burn.
Herman did some good work explaining all this. Take a look at his website.
http://www.users.bigpond.net.au/hermanzone/p17.htm
Now, we have another problem. Well, a challenge anyway. With only 256 MB RAM your PC may not be able to digest a LiveCD. The "alternate install" CD is probly a better choice. However, the "alternate install" CD doesn't have the option of checking the CD for errors. Let's see if we can get a good CD first, then go ahead and try to run it. I just want to warn you ahead of time that it might not work.