LGA775 board? I repurposed a damaged Inspiron 530 (rev. A board, had socket 775 also!) that was donated to the repair shop I worked at. Bought a Core 2 Duo E8440, DDR2 RAM (be very careful about supported RAM speeds, match latency/CAS, and max supported RAM with older boards!), GTS450, and an SSD all secondhand/refurb. Only thing that bothers me is the Logisys PSU, it was a shop spare (Black Swan, 500W I think?) and is essentially a 50/50 part. It's $20 new MSRP online, and sometimes lasts 1-2 years (YMMV).
Runs most modern games smoothly at high resolution for a machine rescued for less than $80. If you're looking for parts or prebuilt/barebones machines, I'd recommend using Newegg in conjunction with PC Part Picker.
If you don't want to deal with compatibility, check out their SuperCombos, often you can score well-built machines for cheap there. If money is a concern, stick to AMD parts. Performance is virtually equivalent to mainstream Intel chips, especially if you start looking into their APUs, which combine onboard video and one of their CPU models.
Good luck! Post if you need more tips or help.