Older Mac games on a an Intel-based iMac

If the games only contain PPC code then they may still play as long as you have Rosetta running. When you first launch the game it may tell you that Rosetta is needed and give you the option of installing it. Depending on the complexity of the game it may work or not you'll just have to try.

For games that run only in Mac OS 9 or earlier, as any from the 90s would be, you're out of luck. There's no way that you'll be playing those on your Intel Mac. Folks may chime in and recommend SheepShaver, but this is a finicky bit of software and it requires that you capture a ROM image from a machine that is capable of running Mac OS 9 or earlier... and if you've got such a machine, you're better off running your games on that machine.

Seconded. Emulation is the only way to run Classic games on Intel Macs. Rosetta is the framework that allows Intel Macs to run PPC Mac programs (for OS X). Before the Intel switch, Mac's also used something called the "classic environment." This allowed OS X users to run OS 9-compatible applications in OS X, but this is impossible under OS X.

I don't have any experience with SheepShaver. I believe Q (which is Mac port of a emulator called QEMU) can emulate PPC environments (I know QEMU can; so I can only presume Q can). But as the previous poster mentioned, the only legal way to get the ROM images you need is by actually owning a PPC Mac.

I'm curious... What game(s)? Maybe there is a new version or a specific port or something. I have a few old DOS and Windows games that have since been ported to run on my Intel Mac.