Have you checked your version of ForceWare? According to NVidia's site, the latest for Vista 64 bit is 163.75, released on 11/06/2007.
Also, what about any Vista 64 hotfixes? There are several Vista hotfixes for GeForce video cards - eg.
http://support.microsoft.com/kb/940105.
I'm not seeing anything remotely like this with SHIII or SHIV on Vista 32 bit
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Acer Aspire e380 = AMD Athlon 64x2 4800+
2Gb RAM, 400Gb SATA HD
PNY GeForce 8500GT 512Mb video
Samsung 216BW
SHIII, GWX 1.03, SHCommander
SHIV, NSM 3.3 classic, LBO