could also be that ubuntu does not have the proper NTFS mounting tool that linux would require.
try this link, first one with a fast google search:
the bit you are really looking for as that thread is from 2006 is this bit:
sudo apt-get install ntfs-config
without the ntfs-config or more likely now ntfs-utils you will not have full read/write access to your WinXP drive.
as unSpawn mentioned above we need much more details to help you solve your problem. copy/paste from the command line the exact code you are using and the output from the computer errors and all.