Yes you move the stores very easily which can be done by going in to exchange system manager expand servers>servername>firststoragegroup(or your storage group name)>right click on mailbox store and select properties abd on the database tab browse for your desired location and exchange will move them automagically.
But before you do that it is possible and and its seems unfortunately, likely lately that your out of space because you have not done a full backup of your exchange stores and the transaction logs are consuming a ton of space. if in the exchsrvr\mdbdata folder you have several hundred meg or a few gigs of 5mb files then that is your issue. do a full backup with windows backup or another exchange aware backup solution and youll free up that ton of space for all logs will go away(except for ones that get created from new transactions during backup)
I am truly sorry to suggest this as a possibilty in your case but i have seen this many times so i am throwing it out there. Again im sorry and disregard if it doesnt apply.
if you feel backup is a burden and not required on an ongoing basis (another issue completely - i wont go there) then you can doe this full backup once and then enable circular logging which will ensure that these log files will not accumulate and worry you with such trivial things such as data integrity :-)
