me personally i have always made my boot partition 100mb regardless of HD size, as of tmp well again personally i have made mine 2gigs on a 60gig drive, and there is probably only about 100megs used ... so depending on how you do things, you could get away with a 1gig or even a 500meg partition ..
again it depends on how you do things, if you were in my shoes, you could get a way with a 250meg partition, cause i over guessed at the time when i made mine