If you're set on doing a completely clean install, the best way to migrate your data is to use a cloning utility (Carbon Copy Cloner is donationware and much-loved) to clone your entire boot drive to an external. Then wipe and clean install. The first time you boot off the freshly installed OS it will ask you if you want to migrate data from an older install; say yes and point it to your cloned external drive. It should import your user(s) and all settings.
You can also have it import all your apps automatically, though were I going that far I'd probably reinstall everything from a fresh download; a little more time-consuming, but it will mean you won't reinstall anything you no longer care about, and it's a chance to make sure everything is updated to the latest version (particularly since you're doing a major OS update--in some cases you might need to update to get a particular program to work right).
Of course, you can also just do an "archive and install" (which is what you'll automatically get if you install Snow Leopard without specifically doing a wipe). That migrates all your old stuff but lays down a fresh copy of the OS.
Final note: If you're going to use the clone-wipe-migrate method of install (or really anything that involves erasing your data off one drive), you should REALLY have a second backup of any particularly important files. Good opportunity to burn all your irreplaceable photos and your novel to DVDs.
Because it's not a backup if there's only one copy in existence, even if only for a few hours--never forget Murphy's Law. Seriously--if you really care about the data, minimum two copies at ALL times, no matter what. Better paranoid than missing files you'll never get back (or out literally thousands of dollars to retrieve them).