Mmm... There are three things I use:
1. Microsoft Excel help
2. Windows Scripting Host reference downloadable from download.microsoft.com (it also contains complete jscript and vbscript reference)
3. Google

))
There is no better way to start learning VBA than to record a macro and dig it with a help opened in a second window

For a programming related information try
www.codeproject.com. There are plenty of examples and "getting started" manuals there.
As for this task with external processing of excel workbooks the main idea is that excel application can be run invisibly and quietly as an ActiveX object almost from anywhere.