How Do I Format My MBP And Keep My Programs

Ever since I installed Leopard last December, my MBP has become noticeably slow and glitchy. Programs seem to crash a lot more as well. I installed Leopard right over the top of Tiger instead of doing a fresh install. Also, any help with formatting my MBP hard drive would help as well.

I would like to format the hard drive on my MBP and do a fresh install with Leopard. But I want to keep the programs I have installed and my email, contacts, etc. Any easy way to save this data somewhere, so I can reinstall it at after my install?

I have already put the .dmg files for most of the programs I have installed in one folder. Can I just copy them to a external hard drive and install them after my reformatting? Please help.

EDIT: I found in this thread that it may be possible to use the backup files from Time Machine. Would this work also after a fresh install of Leopard? That way I wouldn't lose any files or programs. If found some info here: http://forums.macrumors.com/showpost.php?p=6059201&postcount=9