There isn't a good solution to this problem. There is no "good" way to play PC games on a Macintosh. The only way to do it is emulation, and you've already tried the fastest emulator -- if that doesn't cut it, nothing will.
I recommend getting a cheap PC capable of running the games that aren't available on the Mac. Of course, there aren't that many that aren't available for the Mac. Most of the new big name titles are coming out for the Mac as well as for the PC and consoles.
Just search Apple's site for games or check out sites like MacGamer (http://macledge.com) for a list of available games out for the Mac.
Believe it or not, there are Mac games. I'm playing TrueCrime: Streets of LA right now. I last finished Splinter Cell (the original) which was brilliant. And if you have a powerful Mac, you could have a go at Doom 3. Or Sims 2. Or dozens of other top games. Or several crappy games if you're into that kind of thing.
Don't think Virtual PC will turn your Powerbook into a PC. Not really.