What size partition in order to play L4D?

[himwhois]

Hey, I have a MBP and am looing to play L4D. I was wondering how big of a partition to make for it. Currently I have a 15gb partition with windows xp on it. Is that big enough? Would increasing the size make the game perform better? L4D would basically be the only thing I use windows for. Thanks!!!

 

[slpdLoad]

15 should be good for only L4D + OS. L4D is like....7-9 gigs now with the expansion.