the way i've been leaning on this stuff lately is, i put windows and windows related software on c: . that means the security stuff, firewall, anti-virus and so on. c: is my windows drive, then.
on d: i put all my graphics PROGRAMS. note that i capitalized that. DATA, i put on another partition, when possible. thus, psp and photoshop are on d: but all the images get saved in f: . i also have a partition dedicated to music software and music and another for games and one just for saving downloads (sort of my storage closet). each of thoee partitions is at least 100 gigs, some more. i found years ago that i tend to fill partitions way too fast, so i tend to make them larger any more.
i also have a terrabyte usb drive just for backing up all the others. this is normally left off so as not to wear it out.
some folks put all data files on a separate partition, even saved games. some just cram it all on c:, though i find that a bit strange, unless you only have one small partition.
there isnt much advantage in seek time to make just small partitions, if any. and if you're doing anything like the way i'm doing, then you dont want to run out of space on that dedicated to whatever partition. so, however you're going to do it, leave yourself plenty of space for expansion and get a backup drive or system as soon as you can.
If wishes were horses... there'd be a whole lot of horse crap to clean up!
Craig