A Mac mini is decently fast.
Get the new one with DVD burner.
Anti-virus is suggested as is Applecare, but if you get neither, you probably have a 99% percent chance of no issue. This is my opinion having been Silicon Valley trained as a tech and network engineer, and worked on home and corporate workstations in the thousands (Mac and PC).
XP is fine, especially on newer machine, but if you can get a Mac. My 2 cents.