This again, is one of those "WSS 3.0 to Foundation 2010 how to's" that skip 99% of the migration process and endlessly jabber about 1% of it. This only works 100% if the WSS 3.0 site you migrate is as empty as the Foundation 2010 site you just installed.
For just about everybody all "how to's", all Microsoft websites can be skipped because all the say is: attach the old content database to the new site.
BUT! What you really should do, is first check out all those webpart crap you're used to, because Foundation 2010 needs that installed first. Also, things you coded yourself, like a "cross site lookup" thing will break if you don't work out how to take that allong with you. You need to do al of planning and checking if you want a working website, without getting every unlisted error out there.
I've done a migration once and now have to do it twice. Incredible, what a nightmare.