Then Counter-Strike: Source isn't even remotely related to the problem, why bother mention it, and more so when we ask what you're mapping for, why state that you're trying to make maps for Counter-Strike: Source? You're just shooting yourself in the foot here support wise.
Also, because this forum uses a different system it's understandable you don't understand the edit system, so when you post something it puts a edit button next to your username [only if you're the last person to post something], please use this function from now on.
As you don't have a ATI graphics card, that is unusual that you have the infamous 'select behind' glitch, are you sure you're not actually using ATI Graphics Adaptor, and not the Integrated SIS Chipset?