for what it's worth, I would definitely go with VB because you're working with something that's very popular and well supported - much bigger user base, documentation, abilities, etc... I make it a general rule to try to avoid less-common, proprietary compilers or development environments for this reason; you never want to hit a wall where there's something you just can't do with it, and have to wait around for developers to add new features that may never come. You seem to like BASIC, but if you ever decided to use a C-based language down the road, C# is very similar in functionality to VB, practically the same except it uses C-based syntax instead of BASIC, so it would be a pretty easy migration.
And I can say from personal experience that serial port interfacing is really easy with .NET 2.0 - little more than drag and drop, tweaking a few parameters, and writing a small handful of code. It's far easier than the older methods using MSCOMM or proprietary, third-party DLL's or anything like that. The Express edition you linked has all that stuff built right in, and I'd say it's a good choice. I made a little two-way serial terminal application a year or so ago (in C#, but again, practically the same thing) in just an hour or so, on my first try.