jxp1, Thank you for using the Dell Community Forum. The Prescott processor does support 64 bit computing. So, it probably will work with 64 bit WIN 7 OS.  Dell has not tested win7 on this system and has no Win7 drivers for this computer.
Does anyone know if Windows 7 64 bit, will work on the Optiplex GX620 2800MHx MT?
Windows 7 64 bit