I personally used the 64-bit one in 64-bit Windows Vista and Windows 7, both work.
You have to set the pointer speed in the middle (mark 6 of 11), and disable acceleration (as you already know). This will give you perfect 800dpi 1:1 mapping. After you do this you can close SetPoint (personally I don't like the other features and they cause conflicts).
To do this automatically when the system starts up you may run:
If you do that it'll launch, set 800dpi and exit immediately afterwards.
Come to think of it I don't think setpoint ever supported the MX500?
I didn't know the g1 used the same sensor as the 510. I know that the MX310 did though, but I think it's 400 by default as well. Apparently setpoint worked with the 310 too. It truly is a shame that logitech stopped supporting these mice.