You might have some problems running ACT! 6 on Windows Server 2003 but if you are only hosting the database on the server you should not have any problems. You do need to make sure that opportunistic locking is turned off on the server or else you can experience database corruption. If ACT! 6 is installed on the server, run ACTDIAG there and in the File menu, use the opportunistic locking option.
Roy Laudenslager
ACT! Certified Consultant
Techbenders
royel@techbenders.com