xomanowar82 :
i am looking for a server i could play around with. my budget is 300.
also can i use a regular desktop as a server as well
Like Brett said, you can pick up a server to play around with for a few hundred bucks off eBay. New servers vary wildly in price depending on what you need them to do. If you want to serve up a personal webpage, a $60 Atom setup can be your "server." If you want an 8-CPU system for doing massive fluid dynamics calculations, those can cost six figures. If you already have some familiarity with the hardware, pick up used stuff on eBay and put it together yourself. You can find lots of CPU(s) + RAM + motherboard combos from about 2005-2007 or so going for very little money if you poke around a bit. My HTPC has server guts; it has a motherboard costing $30 and the CPUs (essentially a pair of Core Duos) cost $12 apiece. I got a box of assorted RAM for it, which cost $20, and most servers from that time period use the exact same PSUs a current desktop will. Ironically your heatsinks are usually what costs the most as eBay sellers tend to either not include them or include a passive rackmount heatsink you'll need to replace with a desktop-style active heatsink if you are going to be using it in a tower case.
You can use a desktop as a server as long as it has enough grunt to get your job done. Low-end servers often use hardware very similar to a desktop. The biggest difference would be the OS, you can't do much for serving files or webpages using a non-server version of Windows. If you want to use Linux, you can do whatever your hardware will let you do.