What areas to focus on

Question

Hello,

I have an urgent need to create an EXCEL spreadsheet program using C# and i need to create some kind of user interface to this spreadsheet that can filter and prompt the user for information, ie list box, textbox, buttons ect.

I've been searching for examples on the WEB and i'm finding alot of examples that reference .NET, but since i'm not planning on using the WEB for this desktop application, will the .NET examples pertain to what i'm trying to do?

I quess i'm looking for some "buzz" words to reference and to study up on, for example, should i be using .NET vs Application approaches?, or should i be using FORMS? and one huge thing is will i now need to buy the Office product APIs in order to write C# programs for EXCEL? 

And real current worry is now that I finally got Visual Studio 2005 Professional installed, when i try to run some of the existing download examples, VS5 is saying the example can't be converted!

Thanks very much for any pointers,  insights, references, do's and dont's, hints, suggestions, pitfalls, avoidances, warnings, kickstarts ect.....!

BobK