Ditto on that, but given the choice I'd recommend nVidia or Matrox. Their drivers have been a tad bit better than ATI's, in my experience. Even old Matrox cards have very strong (spelled beautiful) analog output and rock-solid drivers. If you're considering Vista, at all, on these workstations go with nVidia or ATI.
ATI's drivers are fine if you forego the Catalyst CC and stick with the driver only, in my experience.
I've found that even cheap nVidia GeForce FX 5200's (weaker nVidia models) do just fine with Vista's Aero and they're vga dual-head as well as possessing extremely stable drivers that seem second-to-none. ...so they'd probably do just fine on those corporate desktops. We buy a lot of this model where I work for the same purpose you've described.