Well, I managed to resolve my 16GB limitation. Its pretty simple infact..... just reinstall Exchange Enterprise over the top and it will preserve your priv, pub, log file etc. I have done this on our production servers and havent had any issues since.
with regards to the last post... eseutil is in the exchsrvr\bin folder and its a useful repair tool - beware !!! dont use it if you dont know what you are doing, it will screw up your database if used incorrectly.
If you have free space on your server, the you can run it on teh same server, if not you could run it from the server and using the /t switch point it to the server with more space or copy the priv or pub to a different server along with this file (eseutil.exe) and defrag it there and copy it back to original place, replacing old priv or pub files.