A new mobo would certainly help in speeding things up, and the old K7S5A is a bit dated, so it would certainly be the a good investment.
What I was trying to say in my previous post was that the mobo isn't the only thing you need to think about. It all boils down to time/money and return on investment ( but a good modern mobo is probably the best place to start, note start not achieve).
Probably the best place to look for a mobo (the one above is rated highly) is in reviews (mags or online) and see what everyone else is using.
But remember its the little things (like only using good quality/high speed memory or cooling etc) that can wreck your chances of creating a demon speed machine (or forgetting to turn off AV, firewalls and anything running in the tool tray/background services).
Oh and don't forget your sound card is just as critical when playing games as all the other components (ever wondered why some tests are done without sound?) when played in the real world (not synthetic benchmarks), and take most 'posted scores' with a MASSIVE pinch of salt.
Have a read of this thread: