For the most part, you'll need a new copy of XP/Vista/7 or even Linux to make this thing functional again. That's probably the cheapest and easiest route here.
Your girlfriend could probably ask someone at the IT department of her employer to wipe the drive clean, but technically they should have done this before letting anyone walk off with the system. There's likely software on there licensed to the company which you're not entitled to use, and could get your girlfriend's employer in a lot of trouble. So, I wouldn't expect it to be very likely that they are all that willing to do anything like that.
My girlfriend got me a free PC desktop they were going to throw out from her friend's company.It's on XP Pro, and I don't own any XP CD's and I've already tried to look online to see if I can boot from a USB flash drive but I can't find anything that works. It's stuck at the company log in screen, choosing whatever server it is they log into or just the computer. I;ve tried every combination of admin/administrator passwords no passwords, etc. But I can't log in. I've already tried to boot up safe mode, but the screen still shows up. Is there any way to bypass this or am I gonna have to aquire some windows discs and reformat?