I have been working with Excel/VBA on and off over the past two years and have been very disappointed in the quality of the basic documentation. The "help" file is almost worthless. The MSDN version of the same thing is better because it has better internal links, but still quite thin. Here are some resources which I have found helpful:
Writing Excel Macros with VBA, 2nd Edition by Steven Roman. Chapters 5-8 have a decent "tour" of the language (you can find snippets in Google Books):
http://www.amazon.com/Writing-Excel-Macros-VBA-2nd/dp/0596003595#noop
The VB 6.0 Programmer's Guide, which mostly also applies to VBA:
http://msdn.microsoft.com/en-us/library/aa716285(VS.60).aspx
There are also various Excel "guru" consultant websites out there that have a lot of example material. Much of it is pitched Excel in general or to non-programmers, but can still be quite useful for picking up VBA in general. Two such sites in particular are from Chuck Chip Pearson and Charles Williams:
http://www.cpearson.com/excel/mainpage.aspx
http://www.decisionmodels.com/
I was about to type a disparaging comment about how I never found a VBA language spec, but I figured I'd Google it again and lo and behold, from only just about a year ago:
http://msdn.microsoft.com/en-us/library/dd361851(PROT.10).aspx
This might contain the answers to some questions I have resolved only by experimentation and encoding the results as unit tests...