you need to make sure it has firmware version 1.4, which has TRIM support for Windows 7.
Most drives come with FW 1.4 pre-installed now but it's easy to check, sort of. You burn the FW 1.4 .iso to a disc and then boot from it. The utility will tell you what FW version is presently installed, if it already has 1.4 just exit out, if it has the older 1.3 then proceed with the flash.
General Discussion FW 1.4 Series VERTEX and AGILITY FW UPDATERS
note: you'll see FW 1.5 mentioned, this FW has support for Trim (Win7) and Garbage Collection (Vista/XP), I've seen a few reports of Data Corruption with this FW so it would be wise to skip it for now.
Once you have FW 1.4 you should do a Fresh Install of Windows 7. You maybe able to Ghost your old drive but I haven't tried it with a SSD. Everything I've read advises a Fresh Install.
After Windows 7 is installed you should run the SSD Tweaker.
SSD Tweak Utility download from Guru3D.com
Edit: Make sure your SSD is hooked to SATA port 1.