That iMac is a good performer, and yet I would try for a lower price on it if possible. If you're not taken by the idea of a tower and you just want a convenient little workstation, go for it.
Go to lowendmac.com and click through the Mac profiles link in their top navigation bar. You'll find a write up and full specs on any machines you might consider.
If you are comparing an iMac and a tower, apart from the FSB and the expandability, consider a few other things:
* If the CRT fails, and they sometimes do, you'll end up having to plug in another monitor anyway. If the analog board fails, you end up with a paperweight or a hack project.
* The G3 in the iMac usually has a smaller cache than those in the towers. I would knock roughly 50 to 100MHz off the performance comparison for this reason. In other words (and this is very approximate) I would compare the value of a 500MHz iMac to about a 400-450 MHz G3 tower.
* G4 CPUs run OS X much better than a same-speed G3. The GUI really speeds up from the Altivec graphics instructions in the G4.
* The CPU in the iMac is not removable/upgradeable. The ones in the towers are.
* Same goes for video. All the towers can take faster and better video cards, which again will help with speeding up the GUI.
All said though, it's a personal choice, and if the iMac is what works best for you, do it.
And if your work is running your Mac Minis on the "bare min" required for Leopard - and I assume you mean minimum RAM - for liberty's sake, get them to double it, at least. The more the merrier. They're wasting money paying you to wait while it spins the beachball.
One more thing? We tend to speak English here, not lolspeek.