If you're thinking about VMware Workstation, version 6.0.4 fully supports Vista. I'm using it myself on Ultimate-32 and it runs just fine. From VMware's web site:
New in Version 6.0.4
Workstation 6.0.4 adds full support for the following operating systems:
32-bit and 64-bit Windows Vista SP1 as host and guest operating systems. Editions include Windows Vista Enterprise, Business, Home Basic, Home Premium, and Ultimate.
Note: The Integrated Virtual Debuggers support most of these Windows Vista SP1 operating systems:
Eclipse Integrated Virtual Debugger can be hosted on all 32-bit versions of these Windows Vista editions. It supports 32-bit and 64-bit Enterprise, 32-bit Ultimate, and 32-bit Business editions as a guest.
Visual Studio Integrated Virtual Debugger can be hosted on all 32-bit and 64-bit versions of these Windows Vista editions. It supports 32-bit and 64-bit Enterprise, Ultimate, and Business editions as a guest.
It's Workstation (not server), it's not free (I paid for the upgrade from VMware Workstation 5 to get the Vista support) and I assume it has signed drivers for Vista 32 (no complaints/prompts during installation). I'm using this on Ultimate 32 every day (work related) and have not seen problems so far...
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Crucial MX100 CT256MX100SSD1 256GB SATA III SSD (User Tree)
2 * Seagate Barracuda 7200.12 ST31000528AS 1TB 7200 RPM SATA II Mech. HD
Seagate ST1500DL001-9VT15L Barracuda 7200.12 1.5 TB S
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AMD A6-5350M APU
Radeon HD (Embedded)
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INTEL Cherryvill 520 Series SSDSC2CW180A 180 GB SSD