it might be safer to go with the 128gb if by SC you mean SC2 and you want to get the expansions later
i'm not sure how much the expansions will take up and you'll want to maintain ~10-20% free space to allow TRIM/SSD maintainence softwares to work effectively
windows 7 64-bit itself can take up 20-35gb of space, and SC 2 with updates ~16 gb
samsung 830, crucial m4, and many of intel's newer SSDs are all good choices
like coup says, you'll want to make sure it's the right height or comes with an appropriate kit