find all instances of text in string
 

I have a string in which I am searching for each instance of the text
"begin*end", where * can be a string of any length. I want to extract each
of these sequences out of the string. So I need a way to find all of them
(doesn't InStr just find the first one?). Also, there is one complication:
"begin" is not always the start of a string I need ... only when there is an
"end" before another "begin". Any ideas? Thanks.