if your motherboard has a Sata controller then yes, you can=)
you should install the 500gb as your file storage drive, and use the 75g for the windows installation only
(or partition the 75g into 2 partitions, 5gb, and 70gb, and use the 5gb partition for windows, then use the 70gb partition for file storage, and the 500gb for file storage)
also, there are new EIDE drives you can get that are just as high capacity as the sata disks
either way, use the 75g for your windows installation, and move all your extra files to the other drive,
this will speed up windows boot, and will help prevent fragmentation issues that will inevitably slow everything down (you can handle waiting 2 seconds for a game to load thats slightly fragmented, but its annoying when your windows installation is fragmented, because it seriously impacts startup / shutdown times)