I've tried to build with msvc 6 earlier, on winxp. Only one obstacle left, as you can see in that thread.
It's possible to use msvc with platform SDKs at least up to and including the February 2003 version (officially October 2002 is the last to support msvc 6, though). To get those old versions you have to either pay M$ to send you a CD, or get it through eMule like I did.
I have no idea about the platform SDKs and win98 compatibility, though. Just thought I'd dump some info here in case it helps.