How do you migrate a WSS2 web site to another server running WSS3?

I've got two servers running Windows SharePoint Services.

Server 'A' is running 2.0, server 'B' is running 3.0.

I'd like to migrate a single web site from A to B.

I found this KB article - How to move a Windows SharePoint Services Web site from one server to another by using FrontPage 2003, and I thought I'd be clever and use SharePoint Designer to try and do a similar thing, but it doesn't work.

You can backup the 2.0 site ok, but when you connect to the empty 3.0 site, the restore function expects a different file type.

It does seem a reasonable thing to want to do, and it's annoying that there doesn't appear to be an obvious solution.