I found a great posting explaining value vs reference types and passing them around (ByRef/ByVal) to methods.

When I first made the switch from VB6 to VB.NET - it took me several weeks to understand the changes in object types and more specifically how they are interacted with when being based byVal - from my VB6 standpoint, I just always thought that if you passed byVal, you wouldn't change the original value, you would be changing a copy of the original value - not so in vb.net. I wish I had been able to review this article back then.