Run Windows on a PowerPC based Mac

No and not really.

You could pick up a netbook, a MacMini, or an under $900 PC even.

Of course you can outfit a robust PC with similar specs to a Mac Pro if you really want to utilize Windows 7 64-bit.

There was an old VirtualPC and some other tools - check Wikipedia and Google.

I have VPC 6 on a 12" G4 Powerbook and use it for simple games, fractals, and Delorme map software. This is the last version by Connectix before the Microsoft takeover. Evidently the MS Version 7 was not very good and had a lot of bad reviews such as this quote from another forum.

"IF YOU HAVE VPC6, STICK WITH IT! Don't upgrade. If you have access to a full version of VPC5 or 6 install those. Otherwise, your best bet is to invest in new hardware."

VPC 6 can be installed on G3 or G4 Macs with OS 9.22 or OSX 10.2.1 ++ and a 500MHz or better cpu.
It comes with Windows XP Home.

While not as fast as the Intel Windows software it works well. You can find examples for sale on eBay by searching for Virtual PC 6 under computer software for $30 +.

Some references:

http://www.macwindows.com/VPC6.html

http://www.macworld.com/article/2810/2003/04/virtualpc6.html

You may also check out QEMU. Not sure if they still have
an active PPC branch. Not as slick and user friendly to set
up as VirtualPC but it is free and may be sufficient to work for you.

Also, if you have a G5 cpu, you have to use Virtual PC 7, as the
lower versions did not support G5's.