I prefer to keep data on a separate physical drive to the OS. If, in the future, you want to do anything adventurous such as fitting a drive caddy so that you can lot in a different drive in order to boot to a different OS, like Linux, then your data is still easily accessible. Also, it is easier to rescue, and possibly a little safer if the OS becomes completely hosed.

I'd make the Windows partition a bit bigger than 100GB too - I used 200GB for mine, and I've already used 64 gigs, just 3 months after installing Win 7.