I'm interested in that too.
What I did:
Install Joomla 1.5
Install VirtueMart 1.1 components and his modules.
I copyed all the jos_vm_ tables from my old VirtueMart 1.0.13a database and insert them in my new database (I did this, because there was said: "There are no changes made in the database"

).
I got following problems:
- My prices are shown without any decimals
- Can't add any products
- The 'GreyBoxes' don't work because I can't save changes made in VirtueMart --> Configuration --> Site --> Theme --> Configuration
- ...
When I install a clean database delivered with VirtueMart installation package, all things called above are working well.
Hope that there will be a solution soon...