Such as?  Don't work how?

It'd help if you could post some representative code and the error messages
that you're getting.

Typical problems in porting code from VC6 include:

- Lack of the 'typename' keyword in places where the C++ standard (and
VC7.1+) require it.
- Dependency on the obsolete <iostream.h> version of I/O streams (use
<iostream> instead).
- Dependency on names being in the global namespace that are now (correctly)
in the ::std namespace.

In converting the project itself from VC6 to VC7 or later, the most common
problem is that of compilation options being converted improperly - in
particular, the project conversion has a nasty habit of turning all of your
VC6 per-project options into per-file options in the converted project,
which can be very confusing when you subsequently try to change project
options and find that nothing's changing in your build.

VS6 is still included in MSDN Professional and above, and is still available
for downgrade (although it's no longer supported).

-cd