I have been using VC7.0 for the longest time. However, this has become difficult due to Ogre moving to VC7.1 and VC8. All it means is that I have to edit the proj files to change the versio from 7.1 to 7.0 and it magiaclly works. However, this is tedious. And some libs, like SQPlus, do not compile with VC7.0. Hence, I think I will take the plunge (and even though I do not care much for VC8 express) and use VC8 - hopefully, that free VC2005 Studio will actually be shipped to me :wink:
As for Linux.. I will set the minimum supported compiler there to 4.0. I do not want to have to garuntee compilablity on older compilers (if they work, great, if not, I cannot help, but feel free to post any errors).
Not sure what the minimum graphics card will be... I have a GeForce 4 which is showing its age - and I can only run a small subset of shader demos. Hence, i want to pick up a newer card and set the reqwuirements to there.. just, not sure which card yet. Of course, there can be fallbacks for unsupported cards (less visually appealling but functional). Though, this perhaps is the job of the material scripts and not too much WGE.
CPU - well, depends on the game itself.
Mem - Game dependent