The exact same thing is happening to me. I just finished a fresh install of Windows 7 x64 on a new Intel 80GB G2 drive. I updated the firmware on the drive before installing Windows. I enabled smart attributes in the BIOS. AHCI has been turned on since the OS install. My motherboard is a Gigabyte GA-E7AUM-DS2H Nvidia 9400 IGP. I also have two 2TB WD Green Drives hooked up to the same machine. All of the drives support smart attributes.
Also, you do need to have the BIOS set to AHCI before installing the OS (cannot switch after OS install). The intel drives need to be running in AHCI in order to use the native TRIM function in Windows 7. If you are using a RAID profile then Windows 7 loaded the matrix storage driver and Windows 7 will not support TRIM. If you are using Legacy IDE (Default) then Windows 7 will not support TRIM. If you are using anything other than Windows 7 AHCI drivers you will have to manually schedule TRIM optimizations using the Intel Toolbox. All computers using a Intel SSDs as a system drive should be installed with AHCI enabled before OS install. Otherwise you are just creating more work for yourself.