If you still own a computer running Windows that you installed from the Dell CD, then you cannot use that disk to install Windows on your Mac -- that disk contains
one Windows license, allowing you to install Windows on
one computer at a time.
You would have to uninstall Windows (use Ubuntu or something in its place) from your PC, then use the Windows CD to install Windows on your Mac. You can't use that disk to install Windows on more than one machine at a time, though.
But I digress -- the CD you have is Dell-specific, and it will only install (more than likely) on Dell-branded computers. I do not know of a way of "de-Dell-ifying" that CD so that it will install on other brands of computers.
While it may be technically possible to "clone" your current Windows installation to your Mac (I don't know one way or another if this is possible), it would be, again, against the EULA of Windows, and thusly, against forum rules to discuss that type of thing.
If you do manage to get ahold (read: purchase) a Windows XP installation CD or DVD that does not contain Service Pack 2 (Boot Camp requires SP2), you can create a new, bootable CD from that installation CD by slipstreaming SP2 onto it. There are numerous guides out there to do this:
http://lmgtfy.com/?q=windows+xp+slipstream+sp2
I think your best bet at this point is to go out and purchase a retail version of Windows XP with SP2 and use that disk to install Windows via Boot Camp. The current Windows install ISO/CD/DVD/whatever that you have will not work, and even if it can be made to work, is beyond the scope of my experience.