hehe... read the EULA (Ed User Licence Agreement) and you'll see that you only own the right to install this on 1 computer (the Dell that it came with). **Not sure you actually own the disk itself** but you definatly do NOT own the software on the CD. I've seen this before. The dell CD's seem to have some way of recognising the manufacturier of the machine, so they refuse to install if it's not a DELL.
There is a reason that CD is called OEM (Original Equipment Manufacturier)... It is only for use with the machine it came packaged with. If you want to have a copy where you can **still not sure if it's legal** install on different machines, but never more than 1 machine at a time **legally** you need to get a retail version.
If you still have the dell machine that the CD came with, you can try popping the HDD into the DELL and installing windows2k there, open the device manager and delete EVERYTHING, shut down and swap the drive into your new machine. This has worked for me several times when.