I've been pondering upgrading to Vista over the last couple of days, but hadn't pulled the trigger because of uncertainty about support for Aero glass on my machine. In particular, I run dual 20" monitors at 1600x1200 resolution per monitor, and wasn't sure if the 128 MB of video memory on my video card was sufficient to support glass in this configuration. Lots of Googling didn't turn up any answers, so I turned to the always reliable win_tech_off_topic group.
Drew Marsh was good enough to point me to this document, which I hadn't turned up in my search. It describes the rules Vista uses for determining when Aero glass is enabled, including the memory and bandwidth requirements for various resolutions and in different monitor configurations. Very useful - thanks Drew.
The good news is that it looks like I'm OK with my paltry 128 MB of video memory. Upgrade is a go!