It is very easy to install Ubuntu on a Xp running computer.First of all you have to find a Ubuntu live cd or dvd because it may not be available at general software shop as it is free.Go to https://shipit.ubuntu.com/ and either download or request a free cd to your residence. If you have win xp installed on your computer and wishing to have 2 os in your computer the easyest way is-R-click on my computer,go to manage.In manage go to disk management and delete a partion from your hard drive (simply r-click on a partition and choose delete logical drive,before doing that move your important files and documents from that drive or partition). Insert ubuntu live cd in your optical drive and restart and boot from the cd.After boot choose install ubuntu from the list which would be appeared after boot.after some easy steps when you will asked for to choose a location to install choose the free space you created earlier(when you deleted the logical drive) amd install. N.B--If you want to make your ubuntu desktop to a cool and eyecandy desktop like win vista ultimate read my other documents.