Try this, from THEBERBSTERS
SH4 <> TUTORIALS <> HOW TO DO IT <> INFO <> DOWNLOAD LINKS -STICKY INDEX thread.
GPU Driver Roll Back To A Previous Version
I don't know as we've seen the issue where the Campaign files do that, but the Single (Quick) Mission and Patrol files don't... I'll send Peter a PM also, and he'll probably be on here as soon as he gets a chance to go over your details, and maybe have other ideas for you...
Edit: forgot to ask you DoctorWho4... Had you tried a "Compatibility mode" or "Run as administrator" from the SH4.exe file's "Properties" page?... thanks!