Airport Extreme + USB Drive vs Time Capsule The price between an airport extreme and 2TB Time Capsule is quite a lot (£100) and as far as I can see the only different is that the Time Capsule has a hard drive built in. 
Is there any problems with buying an airport extreme and a (£70) 2TB USB hard drive and just plugging it in to the back? Will I still be able to use Time machine? And will I be able (like my last question) be able to use the same drive for windows backup?

(I'm not sure why Apple would charge so much more if you can use them separately?)
According to Apple, Airport Extreme with attached disk is not supported for Time Machine. It might work, sometimes, but with a backup system, people usually want more than "might work sometimes".

Sources:


http://support.apple.com/kb/HT2038
http://docs.info.apple.com/article.html?path=Mac/10.6/en/15139.html
http://docs.info.apple.com/article.html?path=Mac/10.7/en/mh15139.html