My brother uses his G15 in Vista and hasnt complained of any problems.
Soz I cant tell you more, he doesnt tell me much cos I think he's jealous of my Saitek Eclipse II
I have seen that the digital display works well while in the games he plays.
Works perfectly on x64 Vista here...just grab the drivers off the site if at all possible. I never use installation CDs anymore if there is an online alternative. It's usually updated more recently, and I can get a specific installer.
You won't need a driver disk to use it like a normal keyboard. Installing the drivers just gives you the fluff, and there are Vista drivers you can download from logitech.
And yeah, if you're installing fresh, I'd always recommend checking the vendors site for newer drivers. I think the last time I used a driver that came with my hardware it came on a floppy!