.NET 3.0 was .NET 2.0 SP1 plus some additional assemblies. If you installed it, your .NET 2.0 applications would start using the service pack versions.
.NET 3.5 was .NET 2.0 SP2 plus .NET 3.0 SP1 plus some additional assemblies. If you installed it, your .NET 2.0 applications and .NET 3.0 applications would be using the service pack versions.
The big difference is that .NET 3.0 and .NET 3.5 was avalible to all OS that supported .NET 2.0.
.NET 4.0 used a different CLR, so I don't know that it upgraded any of the .NET 2.0, 3.0 or 3.5 assemblies.
It appears that .NET 4.5 is something like .NET 4.0 SP1 plus some additional assemblies.
The only configuration for .net 4.0 (but not XP) using Visual Studio 2012.
Install Visual Studio 2012 (and by extension .net 4.5)
Windows 7 (Or Higher)
This is not a Windows XP solution. Just .net 4.0
You have to resist the temptation to just debug on your Machine1