Technically (not legally), there is nothing in the reinstall discs that will prevent you from doing so. But you must do a complete reinstall of both operating systems to use the Dell discs. You cannot simply swap hard drives without significant problems.
I have a Vostro 400 Q6600 with XP Home (SP3) that's a year old. I just bought a Vostro 410 Q6600 with XP Pro. Since the 410 has much more case room I would like to put the XP Home on the 410 (for my home PC) and the XP Pro on the 400 (for my work PC).  Thanks for any help & suggestions!   NOTE: We have programs at work that won't run on XP Home or Vista - they require XP Pro for some reason which is why I need Pro on the work computer.
Swap OS between two Dell Vostros? (Win XP Home<-->Pro)