Let me add one thing: I think that the controller on the motherboard needs to be set to AHCI mode to pass the TRIM command. Otherwise, Win7 can generate it but the drive will not get it. You can check the controller mode in BIOS.
If your controller mode is IDE, don't just change it - windows won't boot. There are several threads here on the registry entry to change just before shutting down IDE mode for the last time.