I do not believe Dell uses a different PSU then a normal PC,
That's actually not true. They do use PSUs -- at least on some models, I know -- that can't be replaced with just any ATX PSU. But I don't know how far back that goes -- if that was true of Dell's models from 4 years ago or not.
Assuming you need a unique PSU for it, however, I know that PC Power and Cooling (PCPowercooling.com) makes replacement PSUs for Dells. And they're probably pretty good, as PCP&C doesn't make any junk. You might check out their Web site and then call or e-mail them re your specific PSU. I'm not an expert on this particular sitch, but I seem to remember some folks saying that the Dell PSUs having a proprietary connector or two that creates this sitch. They also might be slightly odd-sized, preventing a standard ATX PSU from fitting in their designated space. But don't hold me to that as I'm not certain.
BTW, if you're still using a P2 machine, you really might wanna consider upgrading rather than putting any money at all into that old & slow of a machine. Prolly won't be long before the HD dies, followed by some more things soon after. It's prolly got an old 5400 rpm HD in it too (aaaaack! :Q). And like toattet said, it's prolly more than 4 years old, actually.
Welcome to the forums, BTW. Good luck.
Ken