Well actually there were a few ways one could do it in XP, they can probably be done in Windows 7 also. But they are not very elegant solutions (they give bsods) and I wouldnt suggest them to anybody. In XP days there also used to be this shareware called NoSafeMode, but that would enable/disable all safe mode, with and without networking. Dont know whether its compatible with or safe to use in Windows 7.
But again safe mode is a great safety net. If you want to restrict drive/network access, explore other ways.