Project being built on
Would it be more convenient for me to build it using Visual Studio 2005 or Visual Web Developer 2010 Express? I.e., is VS2005 useless for web development projects since Vis. Web Dev has all the fancy new stuff?
Visual Studio 2005 is fine for Web Development as long as you want to target the .NET 2.0 runtime.
With those requirements though, I would definitely check out Visual Web Developer 2010 Express. I think you'll find that it gives you a much nicer coding experience. Depending on exactly what version you target, you'll also get access to features like LINQ which are extremely helpful.
It isn't useless to still use VS2005 but if you aren't using any of the features that come with the full version (vs the express version) you might as well take advantage of the IDE enhancements in 2010. The better rendering within the design view alone is worth the difference.
This depends heavily on what you are doing. It sounds like the only part of Visual Studio you are taking advantage of is Visual Basic .Net and ASP.Net. Both of these are supported products in the two versions of Visual Studio you mentioned (2005 and Web Developer).
The 2010 version of VB.Net has substantial language improvements over 2005 including LINQ, anonmyous types, lambdas, etc ... These are fairly compelling features and IMHO are worth switching to a new version of Visual Studio to use.