Hi Karen,

You won't regret it, Ubuntu is a real pleasure to use. Regarding your problem I am not sure what you are refering to. Usually you have to resize the windows partition, but the Ubuntu installer will not "detect" XP. Have a look at the following (random) tutorial :
http://www.wikihow.com/Dual-Boot-Windows-XP-and-Ubuntu

Please make sure to backup your disk before proceeding with the installation though. I have never experienced any issue when resizing a partition with XP, but you never know. If you get stuck, check the ubuntu forum which is very friendly and reactive :
http://ubuntuforums.org/

It may be a better place to ask for help than the NITRC forum for that particular issue.

Best,

Pierre