In general, the conversion from ext2 to ext3 is trivial. It's basically the same filesystem on disk, with ext3 grabbing a specific inode to hold journalling information. In fact, an ext3 filesystem can be mounted as ext2 with no changes -- you just don't get the journal facility. Under ``normal'' linux, to convert an ext2 filesystem to ext3 requires running one command that takes under a second to complete (it just grabs that inode and sets it up IIRC).

So, without being definitive, the upgrade path could be transparent, and should at least be trivial.