I cut my 500GB drive into 3 sections. There's only 468GB formated total capacity, so you may end up with about 970GB after formatting 1TB.
1) 68GB went to OS, this should be more than enough for Vista and associated applications. Note that I set my swapfile to 1GB, you may need more if you don't 8GB memory. Also, if you have multi-DVD products, then I'd install them else where, see below.
2) 200GB to data file (documents, photos, mp3, video). This is my misc dump drive, and I organize stuff by folders in there.
3) 200GB to games, that should be more than enough for most of the games I have. YOu can also put giant applications here, but I can't think of any giant apps that really needs it.
The partitioning issue was bigger when there's not much space, ie. 40GB. But now that everyone has tons of room, I wouldn't worry too much about partitioning. It's all about doing some segmenting so you don't end up too cluttered.
I will get a separate drive later, and then use it as backup file. By keeping your OS in one partition, it'll be easier to back it up.