May be a bit late but I would do it something like this:

lb = "start"
rb = "end"
StrString = a
intStartPos = 0
intEndPos = 0
lastPos = 1

Do While lastPos < Len(StrString)
intStartPos = InStr(lastPos, StrString, lb)
intEndPos = InStr(lastPos, StrString, rb)

Response.Write Mid(StrString , lbStrPosition, StrEnd)
lastPos = intEndPos + 3
Loop

I didn't test the code but it should work.

Greetings Maurits