You should ALWAYS have a good backup of your important files.
As to using the Dell XP CD, I'll guess that it won't work as expected.. Usually, the Dell CD's only work on Dell computers because they have a special identification program which locks them into Dell machines. (It should notify you of the incompatibility immediately upon booting the disc.) Still, IF the XP version is identical to the one on your other computer, it might be worth a try. Sometimes they work. It must be the same PRO or HOME version and the Service Pack should be the same also..
On the other hand, if you are familiar with someone who has a retail version of the Windows XP CD, it should be able to run a repair install of XP, once again assumming the versions are the same.
Hope this helps.
My sister has lost her Windows XP CD so to be able to follow the threads on the fix via this forum, is it possible to use another Windows XP reinstallation CD to recover the corrupt files? I have one that came with my daughters Dell Laptop but the laptop I am trying to repair is a Benq, both have Windows XP! Before I attempt this is it advisable to burn all photos and important docs to cd disk or should they be safe?