ext4 able to boot from ext3 mbr?

[stan]

Hi,

When I installed F9 from the liveCD I decided to use the 
EXT4 file system.  Unfortunately, there was no way to boot 
from my ext3 mbr.  It kept hanging when it went to the boot 
partition.  I tried some playing around but didn't get it to 
work.  I ended up using preupgrade, which worked flawlessly 
but left me in ext3.

When F10 is available I would like to run it in an ext4 
filesystem.  Will this incompatibility between ext3 and ext4 
still be a problem?  F10 will not be installed on the same 
disk as the mbr is on.  If it is a problem, is there a 
workaround?

Just in case, will preupgrade work for F10?

Thanks.