Here's a list of CPUs supported.
https://www.asus.com/Motherboards/P5KPLAM/HelpDesk_CPU/
The QX99650 and QX9700 processors allow easy overclocking, but tend to be expensive. I've seen the Q9550 go for around $40 used.
It uses DDR2 RAM, only 2 DIMM slots, and only supports a max of 4GB. I don't know if the 2GB you have is a single stick, or a pair of 1GB sticks. If the latter, that's going to be problem - you'd want to get a pair of matched 2GB DDR2 RAM sticks if you can get them cheap. If you already have a single 2GB stick, then you need to find another one that's got the exact same timings as your existing one, and hope they'll work together for dual-channel mode.
To be honest, though, this platform is something on the order of being almost a decade out of date. Even if you got all this stuff together relatively cheaply used, you are talking basic gaming.
What kind of games were you hoping/expecting to play, and what monitor do you have?