Upgrade 2006 databases to R2

Hi, we are planning an "upgrade" to R2, the only catch is that we cannot do

the real upgrade due to BT server edition limitations, so we are
reinstalling 
the biztalk instead. But we'd like to keep our databases and upgrade them
to 
R2. is this possible at all? we have 2 biztalk 2006 servers with a sql
2005 
in a cluster. we are thinking about separating one of the biztalks, 
uninstalling 2006 and installing R2. At this point we'll have to go
offline 
until we reconfigure R2 and upgrade the databases. then go online with R2,

"upgrade" the other biztalk and join it to the group. so is it possible to

upgrade only the databases?