Parapunter,
It all depends on the unit. Most Servers are just like any other computer, they just have different software on them. (Usually Servers will have RAID Cards on them so they can have Mirrored Hard Drives.)
If this is the case, then you could just install WinXP on it and use is as another computer.
If the Server is a Rack Mount Server, then things change dramatically. Since your friend is offering this computer to you, my guess is that the unit is not a Rack Mount, since he would know you would not have much use for you.
Take Care,
Richard
P.S. Memetic, it looks like our posts crossed.