Backups using a NAS from Tiger and Leopard

[reprobate]

I'm one of those who bought the Airport Extreme N the day after it came out, then promptly found out that it didn't work with TimeMachine. Guess what? It still doesn't! However, after much thought and self consolation I've decided that I don't really need TimeMachine. SuperDuper! does just about everything I want it to do and with the exception of the occassional document that gets deleted by mistake, I'll be happy with SD.

Now here's my situation and question. As mentioned I'm using the Airport Extreme N for my wireless router. I'm about to buy a Seagate FreeAgent 750 GB external hard disk so I can use it to back up the iMac G5, my wife's Mac Mini in the kitchen, and my iBook which resides at the other end of the house, as well as us it to store my iTunes library. The iMac, BTW, is connected to the router via ethernet, while the other two macs are wireless.

Now, here's the question: With this setup would you think I'd be better off connecting the external drive to the iMac via Firewire and setting up sharing to allow the other two macs to use it, or would you connect the drive to the Airport Extreme via USB and use it as a network attached storage?

I'm somewhat new to networking and particularly to network storage, so I hope I explained everything clearly enough.

Thanks