i'm installing o/s for first time on new custom built computer (by me =P, first one). i have to option to create partitions now, what should i do for optimum performance.

i have 80gb hdd

i was thinking

20gb for downloads and shared stuff on network
10gb for o/s and some software
45gb for games and other software

thats 75gb.. i have like 76303mb to divide... i atleast want 2 partitons, one for shared stuff and one for rest...would it be better (performance wise) to create seperate for games and o/s ??