If you are new to VB.NET, I would suggest starting to get those old adages concrete before you start another major project:
1) Name variables wisely.
rtb1 could be txtUnstrippedHTML ; lbloc could be strLeftPosition
2) Declare variables with specific types.
Dim rtb1? Better, Dim rtb1 as Integer
This improves speed vastly, and helps to catch errors
3) Initialize variables with the declaration if possible.
Dim rtb1 as Integer = 0 ; Dim lbloc as String = InStr(htmlstr, "<")
4) Even though it is possible, try not to declare variables on the fly.
In a large application with hundreds of variables, this can save hours of debugging.
Just my two cents here. Ignore if need be
