When I worked for Microsoft Money 2000, I did a medium-sized matrix for what browsers came with which OSes, and therefore, what scenarios were possible.
Win95original - none
Win95b - IE 3.0
Win95c - IE 4.0 (Yeah, there was an "integrated" version that was released... It was horrible. Trust me.)
Win98 - IE 4.0
Win98SE - IE 5.0
WinME - IE 5.01 (? Don't know - it was not even in full testing until after I left the group.)
WinNT 4.0 - IE 2.0
Win2k - IE 5.0
WinXP - IE 6.0