Hi!
X is the graphics... (like Windows used to be to DOS). If it is an old computer you might try with the ALTERNATIVE version of UBUNUTU, see
Ubuntu Home Page | Ubuntu. That version doesn't contain the LIVE CD, so I suggest you download both versions, and try the LIVE CD first.
The same thing have happend to me a couple during the last decade (Red Hat 5-7 and Ubuntu 5.05 - 7.04)... I had to adjust the settings for the graphic card and then it worked fine. Try again and then use GOOGLE to find the solution for error you get.
You have a lot of help in the UBUNTU forums (also in Swedish at
Ubuntu Sverige | Ubuntu Sverige). Visit the INSTALLATION and NEWBIE groups.
Good luck
/ Kim