My friend is making a large document in Microsoft Excel 20 or so columns. He found that he was forced to go back everytime to the top of the document to figure out what the column represents. In other words he wanted a way to freeze the header row so it is visible everytime. He asked me how to do it. I showed him. I felt other's may find it useful too, however it is hard to express in words (which I anyway tried below). So here is a tiny flash presentation (took me about 5 minutes to create) demonstrating the solution.

Summary
Drag the bar shaped thingamajig from the top of your right scrollbar down below the rows you want to keep visible always. You are done!
If that is not clear see the presentation below.