Laukev is pretty close, but G3's are nowhere near as fast as G4's. Especially for OSX.
OSX will outperform any G3 when running on a G4.
If you are going to get a Mac, consider either a notebook, or a tower. I have sworn off iMacs because they are slow, unupgradable, and when they break, yer screwd.
The towers will never let you down.
Any low end tower will kick the shit out of any PC. Speed wise, well, a 2.4 PIV will be faster genrealy, like Playing high end 3d games and such, but practically, when do you really need 2.4Ghz? I would say a low end tower, now adays like a dual 800Mhz G4 would be a kin to a 1.5Ghz Pentium.
But you must remember, that what you are paying for is not speed, or power, etc. Your paying for an overal package. The Mac is an amzing computer, fully integrated, and infenetly usable.
It's a well oild fine tuned machine with all parts working in perfect harmony. Remeber, Rolls Royce dosn't make the worlds fastest cars, but they sure as hell make the nicest
The Mac, with OSX will never let you down. And I guarantee it will quickly replace your Linux and Windoze boxes.
Not to mention integrate seemlessly with them in a LAN
I have 2 Mac's and 2 Pc's at my house, and they all talk to each other perfectly. One runs Windows Me (yech!), another is Dual booting with Win 2k Pro. and RedHat 9. The Mac's both run Panther. It's a great setup, perfect for the cross platform work I do.