Differences between Visual Studio 2005 Versions

A good starting point for the VS 2005 product line overview is here.

Here is an overview of how Visual Studio 2003 is matching Visual Studio 2005:

If you are looking for more details what each version has to offer go here, here or here.

Here is a short summary :

Visual Studio 2005 Express:
They are intended for neophytes and newbies. We're actively streamlining the Express products to meet the needs of that audience. Everything about Express has centered around simplicity, simplicity, simplicity, simplicity, and more simplicity...and making programming streamlined and attractive for people who have no idea they want to program. Thus the "fun" Starter Kits, the super simple setup, the super simple IDE, the lack of "professional" features, etc.

Visual Studio Standard 2005:
It is basically the union of the Express SKUs with mobile and remote data support added. It doesn't have support for remote debugging or server-side development, it doesn't have SQLCLR support, and it doesn't have the deeper data tools in Pro

Visual Studio Pro 2005
Visual Studio 2005 Pro is including all possible features except the project management tools included only in Team System.

Visual Studio Team System
Team System is Visual Studio 2005 plus a suite of tools which are supporting the entire software development lifecycle. Tools like the Distributed System Designers, will help to model  pplications and logical datacenters. The Team System will include code quality and defect testing utilities, such as dynamic and static code analyzers, performance profiling, unit testing, and code coverage.
Which tools are available depends on your role. There is a Team Architect, Team Developer and Team Tester Role.