Assuming the hard drives are comparable speeds, it would actually give you slightly better performance to keep your games on the second hard drive (though practically you might not notice a big difference). Since games can be fairly memory intensive, Windows will be using the swap file more often (located on the c: drive by default). If games are trying to read or write to the same drive when Windows is doing memory management stuff, it will take longer.
Also, if you are just installing games on the second drive, then it should remain much less fragmented than your Windows partition (especially if you install and uninstall a lot of utility programs, or do other things that add and remove a lot of files). Again, this would not really be a huge effect, unless the drive is very fragmented and a game is trying to read a large file spread across a dozen places on the drive.
