We had an arcade/redemption game running on Win98, but hardware which can run it has finally gone obsolete. The game used a number of scaling effects, some through the 3D path, and played some tricks moving things in and out of video memory. If I was to undertake porting it to run on Windows 7, how much trouble would it likely be? Would it mostly be recompilation, or have the APIs undergone such transformation that I might as well re-write the device interfaces?
Don't think of it as porting to Win7. Just simply port to DX9 and let DX do the work with the Win7 parts. Infact, you could probably just leave it as is and it shuold run -- but you mention you do crazy things with video memory that I assume has nothing to do with DX. (ie either through GDI or some other hack?). Anyway, the DX7, 8 and 9 APIs all have quite drastic differences. But the nice thing is they're all backwards compatible. If the code you have is pure dx7, try compiling against the latest SDK and see if it works on win7 straight off.