Pyroflea already recomended using virtual box, so I am asumming that you want a system with XP and Ubuntu 10.4. You are, thus, talking about dual booting XP with ubuntu 10.4. Then the place to start is the ubuntu forum. Also check this:http://www.psychocats.net/ubuntu/index
It does have a full guide for using virtualbox, using wubi and dualboot.
This thread could be helpful http://ubuntuforums.org/showthread.php?t=1527121
Guides for dual booting assume you have an hd with everithing in it (OS, apps and data) this thread is useful since it deals dual booting using an hd for windows/apps, another for data and another one for ubuntu. Check in particular post 6 and 7. They have some really useful links like http://members.iinet.net.au/%7Eherman546/p24.html