Anyone got it working? I used the installer from the GPL preservation society and haven't had any luck yet. I'm sure there's something I'm missing somewhere though

It works fine.

I just installed GPL from the disk (so the registry entries were there for the editors which use them) then deleted the contents of the folder (C:\Games\Sierra\GPL in my case), then copied my existing install into that folder. It's fine.

Win 7 x64 using an ATI HD 4870 in DirectX mode.

What's stopping yours running? Do you see anything on the screen? Does it crash to desktop? Do you get to the menu?

Basically, with just a clean install, it loads to the menu screen then crashes to the desktop.
With the GPL 2004 demo applied it loads, but the frame-rate is around 1-2fps and of course it is unplayable. Also the resolution seems to be messed up - like it is not compatible with my screen. The bottom half of the gpl screen is past my moniter, if you get what I mean.

The clean install will need the patches to work now (the 1.2 patch, the CPU patch and either the DirectX or OpenGL patch).

The demo will likely already have these. Make sure Cool 'n' Quiet (AMD CPU) or SpeedStep (Intel CPU) is disabled in the BIOS and I think I remember GEM+ having a workaround for it (though I've never tried it).

For the graphics glitch try the other renderer - if you use Direct3D try OpenGL and visa-versa. There is also a 3rd-party update of the Direct3D rasteriser which can be found here.