I would double the ram if I was you...you have one glaring great big problem visible in your system. Line 1 "Windows Vista"
Secondly what kind of video card are you using? First person shooters are very video intensive, its definitely a winning edge to have a good video card, shared 64mb might work, but your fps is going to be very low, which will in turn get you ganked and frustrated! Another thing with CS source...how is your tolerance for hackers and cheats? I stopped playing source over a year ago just because I was going to scream if I saw another person wallhacking!

Source is an old game now, the system you have will play it for sure, but I would definitely invest in some extra ram, one gig is marginal at best with vista.