These days I am giving some presentations on Biztalk 2006 along with a few other guys here.
The 11 days sessions are intended to start from grounds-up assuming that you do not have any background of BizTalk and then take you to an intermidiate level at the end of it.
While hunting for information on migration from the previous versions of Biztalk, I ran into this link on MSDN that gives a very detailed view of what it takes to migrate from Biztalk 2002 to 2006.
As we all know, there are a hell lot of changes in these two versions. But there has been a good effort to support the migration. Of course, its not possible to automate 100% of the process.
Although, I havent tried it out yet, it seems that you can save some considerable hours by using the Migration Wizard.