Minimum Version of Internet Explorer

[CST]

This is a noob question, but is there a miniumum requirement for IE
that a .net web application needs to run (e.g., will a client running
IE 4.01, 5.01, etc. be able to run a .net application)? What about
machine specs (RAM, processor, etc.)? I currently have an .asp
application and heard that migrating to .net would be a complete
re-write, is that true? Sorry for asking such simple newbie
questions, but any responses will be much appreciated.

TIA