If you do a fresh install of Windows 7/8 on a SSD, TRIM will be enabled automagically. It's one of those things that the Windows installer does at OS install to maximize performance on the SSD. Additionally, as Cybs points out, the installer aligns the drive and data on the drive so that performance is optimized.

It's a huge pain in the ass to reload the OS and all your apps, but in the end, if you don't... you won't be getting the most out of your upgrade.