I don't know about IE1 and 3, but for IE2 (the one that shipped with NT4) you need at least, from what I remember:

- no name-based virtual hosting (it does HTTP 1.0 but doesn't send Host headers)

- avoid redundant whitespace (it's not collapsed)

- wrap <style> and <script> contents in <!-- and // -->, otherwise they will be visible

I've had to keep an application's webinterface IE2 compatible ("usable") for longer than I wanted to as the initial configuration (opening up ports and IP addreses) was generally done on the NT4 server in IE itself.

(Once initial setup was done, further configuration could be done remotely with a more 'modern' browser, so fortunately only a few pages needed to be usable by IEs that old)