Changing HD on macbook pro and restoring?

I currently have a Macbook pro with leopard and I want to upgrade the hard drive to a SSD and upgrade to snow leopard as well..

Is there a way I can backup and restore all my files and software on the new hard drive is snow leopard?

I suggest you back up everything 1st and foremost.
Use SuperDuper or Carbon Copy Cloner that way you have a clone of your HD if anything goes wrong, and 2nd if you want to revert back to Leopard you can.
I would then install Snow Leopard on your HD that is in it to start with. Doing this will by default do a archive and install. You will have SL on it with your system the same as you left it, as Leopard.
Then on a separate partition on your External to another clone of the SL system you just put on your MBP.
Then rip out your old and replace it with your new HD. Install SL on it which will only take 40 mins then goto your external and migrate everything over.
There would be other ways of doing it, but this is the way i would do it.

If you have a external enclosure for the new SSD then you can wipe out one of the steps and when SL is on your old drive in the MBP still, you should be able to load up the SSD straight from there ....
If you get my drift lol