Well if you wanted to start coding ASP.NET, the guys over at www.asp.net have written Web Matrix which is a free download.

The .NET framework is free of course and comes with all the compilers you would need, so there's nothing stopping you from starting without using an IDE.

http://www.asp.net/webmatrix/default.aspx?tabIndex=4&tabId=46">http://www.asp.net/webmatrix/