Differences between Visual Studio (.sln) build runner and MSBuild

I'm trying to set TeamCity to do a CI using .Net and configuring build runners I have:

1. Visual Studio (sln)
2. MSBuild
3. Visual Studio 2003

What's the difference? Why three build to work on the same type of project? (With the exception of 2003 which is only for 2003 I believe, Why?)

Taking the issue, we have this build runners for .exe files:

1. .NET Process Runner
2. Command Line

The "Command Line" build runner not works with any .net assembly? Why the .Net Process Runner?