Did you mean VB6 or VC6? (subject says one, text says another).
Of course, VB doesn't produce static libraries, but DLLs produced by VB6
would be just as usable from VC7 and from VC6.
Static libraries produced by VC6 may be usable from VC7 depending on a lot
of factors. What's in the library exactly? A library that uses MFC, ATL or
STL is very likely not usable from VC7 if it was built with VC6.