Unfortuantely that is not legal. I would talk to your boss and see if he would sell you one of those Dells on the cheap. If so, then rebuild it with some upgraded parts (larger & faster hdd, more ram, maybe a better cpu, etc.). It really depends on the model, but if you don't need something bleeding-edge, you could probably do nicely with the old Dell. Having the XP Pro COA, they are probably at least P4 Socket 478.
If you start fresh, then just get all of your parts from some place like newegg.com, and buy your OEM OS at the same time with the rest of the parts. XP Home is less than $100 🙂