if the second SSD you speak of supports TRIM itself, then yes, if it's plugged into the system that's running Win7 with the msahci driver (i.e. the native AHCI driver), it will have TRIM enabled.
Worth checking that 7 doesn't place the storage SSD into the defragment schedule, too.
Thanks for the info, I think I'll give it a try from what you've said. If it's performance isn't that great I could put it into this computer as the main drive.