Simple, but required some faffing for me:
1. Install game
2. Install 9.6 patch (get from here http://www.grandprixgames.org/list.php?28 - it's called 1.02 but open the link and it's the 9.6 patch)
3. Install decryped exe (you'll need it for any mods anyway, also on link above)
4. Use Application Compatibility Toolkit and set GlobalMemoryStatus2GB to true, against GP4.exe
5. Apply Creative's ALchemy against the game folder for 3D sound

Optionally: once you've booted the game and set Graphics as you wish, then tweak away in the game's f1graphics.cfg file, in particular:
; [RELEASE] Game 3D Horizontal Resolution = set to resolution you want, widescreen supported
; [RELEASE] Game 3D Vertical Resolution = set to resolution you want, widescreen supported
; Number of mipmaps (0 => off) v2 = set to 0 to stop graphics being all mip-mapped to hell!

p.s. it might still crash sometimes, GP4 was always a tricky one!
p.p.s. if you briefly see the in-game triangular cursor, then get a black screen, then the opening video isn't working. Just bash the escape key to skip it (as the opening video was always a bit naff!).