you can use pretty much anything 10.3 and newer. 10.2 was the original for those iirc. I had one (it's in pieces should I ever get around to getting a proper board) but I have used Retail 10.3/10.4 and even 10.5 (With a bit of hackery and a DL DVD and DVD Burner)

I would say max the system out and get yourself a copy of 10.4 on eBay. it will hum along beautifully