I've done quite a bit of fairly complex stuff with Excel and OLEing into Excel. All of the above is pretty good advice. What I haven't seen stated is:
1) Excel uses VBA, which is a pared down version of Visual Basic. If you've done _any_ programming, it's probably in some flavor of Basic (C64, Apple II series, QBasic, LotusScript, OracleBasic, etc.). The vast majority of that knowledge will help you, as will much of the reference material for those languages. Of course, anything VBA/Excel specific is best.
2) Cheat! This is the best advice I can give you. Excel has an awesome macro recorder. Record something similar to what you want to do, look at the code it comes up with, and tweak it untill you get what you need. I've been working with VBA in Excel pretty much since VBA was added to Excel and I still do this quite often. Not only do you get something that is nearly a final product, but you get a code sample that you can review.
3) Use the included help files. Sometimes these can get kinda thick, but you can get some good information out of them, still. Using the macro recorder to generate code, then using context help to understand what the code does is usually a great way of figuring things out, IME.