i want to download a game through steam but it says i haven't met its requirements

hi,

i've tried to download a game through steam and it says i havent met its requirements,

its requirements are: OS X version leopard 10.5.8, snow leopard 10.6.3, 1 GB RAM, NVIDIA GeForce 8, ATI X1600 or intel HD 3000 or Higher Mouse.

for the link of the steam page:http://store.steampowered.com/app/440/#game_area_sys_req

All i know is that i have a macmini2,1 with a Intel Core 2 Duo Processor and im running on OS X version Leopard 10.5.8 ( i have no idea what a NVIDIA GeForce or a Intel HD 300 is)

could somebody please tell me what im missing.

thanks

david