Only one drive is required, you may need to use partition magic or a similar program to resize your windows partition to leave some space for a Linux partition.

It is pretty easy to setup and well worth it, a lot of people are happy to run pirate software but with linux you don't have to...

Just google "dual boot ubuntu tutorial" without the quotes and you will find guides, if you like 'eye of the tiger' then use this one :^)

http://video.google.com/videoplay?docid=-6104490811311898236