you need 120- 200g for games..
unles to raid 0 them(pain in the ass), yo would be better of with a fast hdd.
a new generation 500g platter hdd, has 130+ mb/sec transfer rate (for the first 6-200g) (depends on size 500g-2tb hdd)
just partition c as 200g, rest d: (same as short stroking a hdd...