Check your BIOS version to see if it needs updating from the model's Support Downloads webpage.
What is the SATA controller setting in BIOS? Try AHCI, then IDE if neccessary.
Are you wiping the HD when you attempt install? You'll need to boot the installer, select Custom install and use Drive Tools to delete all, create New partition(s), then format before installing to first partition.
I'd go an extra step and clean the HD deeper: Boot Win7 DVD into Repair, open Command Line, type:
SELECT DISK # (replace # with Win7 target HD #)
Now use Custom>Drive tools to create and format your partition(s).