I'm having the same issue upgrading to Ver 9 (2007), after the install process, I put in the serial number and hit the next button and a warning comes up stating "The registration process has detected that Microsoft SQL Server 2005 Standard edition is installed, but the serial number prevents access. Uninstall Microsoft SQL Server 2005 Standard edition and use Disc 1 to re-install Act!, and then register the product."
I did uninstall Microsoft SQL Server and the help files and an SQL Writer? And then went to re-install, actually I repaired Act! (hey, maybe that's the problem).
XP Home Edition SP2, on a Dell Dimension 8400, Pentium 4 3.0 GHz, 1 GIG RAM.
I'm still waiting for my copy of "MENSA for Dummies"