Get the Iomega drive from London Drugs. It has both USB and Firewire (400/800). It's also 500GB and was 199 last time I looked.
Gimme a sec, and I'll get you a link.
Here you go:
http://www.londondrugs.com/Cultures/...7&ProductTab=3
It's actually 179 now.
Edit: Some may say that 179 is too much for a 500GB, but keep in mind this supports FireWire 800 which is the fastest data connection you can get on an iMac or a MacBook Pro. Even if you only have a FireWire 400 port, it's still faster than USB for your Mac. Like everything else that is built for a Mac, it's a bit pricier than other options, but it's worth it. My reccomendation: Plug it into the FW port on your iMac and leave it there, with Time Capsule turned on and running, and then create a secondary NTFS partition that you can share and access with your Windows box over the network.