Personally I would use the Windows 7 migration files to backup all your old files. Reinstall these to your new SSD boot drive when you finish installing the OS. You will still need to reinstall your applications, but all your data should be there. I personally use Mozilla Firefox, so I use a utility called Mozbackup to backup all my Firefox settings, which makes my web browsing experience almost identical from one computer to the next. After all your data files are backed up from your now secondary hard drive, you can reformat and turn it into a data drive. Sure your old drives OS won't work in the new computer, but I still prefer to have the completely intact old boot drive when I do a new install. Having two drives, an SSD for booting and at least one regular drive for storage, is the way to go.
In fact, you might buy the SSD first and try installing it in your old computer. You might find, like I did, that I didn't need to upgrade my CPU and motherboard. The SSD breaths new life into many older computers, but you really do need Windows 7 for the trim support. Upgrading to SSD actually saved me money because I would have been eeking out performance gains by doing costly CPU/motherboard swaps, when the performance gain of going to SSD dwarfs any CPU upgrade I ever did. Sure an SSD doesn't get you raw processing speed, but my god the responsiveness of your system is light years better.