two AMD processor sitting around

To start, the Dell would have come with an Intel CPU, so the AMD CPU wouldn't fit. Next, the old Dell probably doesn't have a very powerfurl PSU. The ram might work, but might also be so old and slow as to be useless. Then again, the ram may not be compatible.

What you have that might be useful is a case, maybe a hard drive, the various disc dives, and not much else. Depends a bit on the exact specs of what hardware that you have. Sorry to rain on your parade, but unless you know exactly what you have, it will make more sense to buy new hardware.

A Dell wouldn't have a motherboard that any AMD DP chip can fit in as Dell only very recently started to offer anything that has AMD chips in it. Depending on what kind of dual-processor AMD you have, you might be able to find a replacement motherboard for not all that much money. You can certainly use the old HDD and GPU, and maybe the RAM (if you know if it's buffered ECC or not and if you need buffered ECC or not for the dual AMD mobo) but the PSU won't work, the case is probably a no-go as well.