Using the video recording function of FRAPS can cause pretty drastic FPS hits. It can be caused by two things, first check to make sure that you aren't limiting the video to 29.97FPS, if you are then that is the highest the game will be played at, I would choose at least 60FPS. If that doesn't help, I can't say for sure if it's a RAM issue, as I have 4GB of RAM and even recording TF2/CSS causes the game to lag pretty badly.