Well.... playing those games on a PCI video card will get you major LAG. I think you need a new motherboard that supports AGP or PCI-e then get one of those cards.
That's the best you're going to do. Actually though, I've seen CS:S played on it, and it didn't lag. It was very fun and playable. Sharp picture and everything. It's not as bad as some people carry on about. They're just used to thier $300 video cards.