bootcamp partition size question

Hey I bought a macbook pro because I am taking graphic design and I was so happy with how easy it is to get windows on here and start gaming aswell, I only have one question and its about the size of my bootcamp partition, the instructions were a bit confusing and I was under the impression that I had to pick the 32gb drive size, is this true? because after installing oblivion, unreal tournament 3, and sins of a solar empire, I'm not left with much room (which is horrible considering I like to mod my own games)

Anyways I would like to squeeze fallout 3 on there and that obviously wont happen unless I have atleast a 40 gig harddrive, I dont mind reinstalling windows/bootcamp and all my games because I format frequently anyways and keep back ups of all my patches.

another quick question is if it is not possible what about an external hard drive? can I install games onto that, and run them in windows? and if so which external hard drives should I stay away from?