There has already been good comments on both sides. As a computer tech I always ask what the usage will be. If you'll be running mostly older software then the G4 would be better. If you in vision needing the hardware that was optional on the G4 but standard on the Intels, more then 2 USB's, multi-media center (i.e front row) etc then the Intel would be the better value long term. People have said that the G4 is a tad more quite. The G4 tends to have a low hum whereas the Intel has more of a low buzz when in use. RAM has already been mentioned the Intel maxes out at 2 GB which is good for photo and multi-media use. You can't ever have too much RAM in a system.
As for the graphics card, I know many say the PPC is better because it has a dedicated card over the Intel's integrated one. An Intel with 1 GB RAM, you really won't notice the difference. I wouldn't run OS X with anything less then 512 minimum 1 GB is better since OS X is RAM hungry. The integrated supports functions & features the ATI card lacks. When you compare them the difference isn't as bad as most people believe. 18 years in the PC world, laptops have had integrated graphics for years. Unless your a gamer, you'll be hard pressed to see a difference. Graphics really isn't a facter unless it's for games. In that case you'd want the iMac or a PC.
It's really a tough call, what I would do is make a list of all the software and things it'll be used for. Get the specs of both systems, then make up a small pros/cons list for both systems. You may see more pros for one system over the other. That may help you to decide, but either way I can't see losing out as both are good systems.
1.66GHz Intel Mini Duo, 1GB RAM, 100GB HD Mac OS X (10.4.8) A,Network Certified