I have an old computer, My old 2007 gaming rig, and I want to turn it into a server.
 
Specs:
 
Amd Anthlon 64 x2 5600+ Processor @ 2.80GHz
Corsair 4 GB DDR2 800MHz Memory
Nvidia Geforce 6600GT 256 MB DDR VRAM
http://www.msi.com/index.php?func=proddesc&maincat_no=&cat2_no=&cat3_no=&prod_no=1143
250GB 7200RPM Hard Disk (sata)
J&W AMD AM2+ Motherboard ATI CrossfireX 
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500w Coolermaster PSU
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DVD/RW Burner (sata)
Windows 7 64 bit Professional OEM
 
Now I don't have the bucks ($$$$$$) to go out and buy a dedicated server, I only will use it for home file sharing, Print Server, Backups of all of the PC's and general storage. I would use it for a game server for my Lan parties that I have once a month with 15 People, And it would be used at the anual Lan party of about 45 people.
 
I Don't have the Bucks ($$$$$$) to get a new mobo, processor or memory yet, but will do that soon. 
 
So what do you think, I'am new to this server thing, But I know Networking and I'am a system builder (Not a Server Builder)
 
What should I be doing?