you may need to first separate the data and OS on your main HDD, like onto separate partitions. then you'd need to spend hours resizing the OS partition until you get it down to be smaller than the SSD. then you'd do a Win7 system-image-backup, make a recovery disk, reboot into the recovery disk, load your motherboard's SATA drivers, and then restore the image from the HDD to the SSD. the hardest part will be separating the OS from the data and 'cleaning up' and resizing the OS partition to a reasonable size.
or you can try a program like Acronis. i've never used it, but heard that it's smart enough to extract just the OS and shove it onto a new drive and make the new drive bootable. i would hope that it can do it without affecting the OS that's on the HDD so that if things don't go according to plan, you can reboot and continue to use the HDD just as before. and then spend untold hours doing a fresh install of Win7 onto the SSD.