Darth,
Thank you for using the NI developer exchange! The AC coupling is not designed for measuring the RMS value of an AC signal. It is just meant to get rid of any DC offset when you are making measurements. The best way to program the DMM-4060 card from Visual Basic is to use the NI-DMM 1.5 driver. You can download this driver from http://www.ni.com -> downloads -> drivers and updates -> current software versions -> NI-DMM. The driver installation includes example files for Visual Basic and Visual C/C++. They will install in the c:\VXIpnp\win95\NIDMM\examples\ directory. If you are using Windows 2000 or Windows NT, the win95 path will be winNT.
Best Regards,
Jace C
NI Applications Engineer