Remember that PowerPC-based Mac OS X apps run under the hardware emulation layer known as Rosetta on the Intel Macs. For this reason, you are able to run PowerPC-based Mac OS X apps. However, the Intel Macs don't support applications that required to be run under Classic on the PowerPC Macs. So if one game was a native PowerPC-based OS X application and another one was a Classic Mac OS game, then the only one that would run (although probably not perfeclty) is the OS X one.
That said, some games might exhibit issues when run in Rosetta. What you can do is check the software developer's site to see if they have provided a Universal Binary for that game so that you can run it natively on the Intel Macs with all the performance benefits. If not, then the only option is to run that PowerPC-based OS X game through Rosetta (which suffers from a performance hit since it is emulating a PowerPC processor in software).
Or, you could use Boot Camp to install Windows XP on a separate partition on your Intel Mac. Then you could boot into that to run a game that wasn't available as a Universal Binary on the Mac or was Windows only.
• Apple iMac G5 17" (2 GHz G5) - Mac OS X 10.5.8/Ubuntu 10.04
• Asus Eee PC 901 (1.6 GHz Atom N270) - Fedora 13
• Apple Macintosh Quadra 650 (33 MHz MC68040) - Mac OS 8.1
• "JHVH-1" (2 GHz AMD Athlon XP 2400+) - Slackware 13.1