This might seem like a perverse question to ask - isn't there only one Beta 2? But keen eyes have already spotted that the WinFX Runtime Components Sept CTP release contains a later version of the CLR than was distributed with the original Beta 2. Here's a quick explanation...
Basically, .NET Framework Beta 2 originally shipped as 50215.45. We made the decision several months ago that we’d try and stabilize for the PDC on Beta 2+ bits, so that SQL Server, the Max demo, WinFX Runtime Components, Windows Vista and others all had a consistent build to run on. DevDiv have integrated a number of non-breaking bugfixes to the Beta 2 CLR to fix bugs that other dependent teams encountered, so the build number has crept up a little, but build 50215.322 is binary compatible with 50215.45. You’ll sometimes hear 50215.322 referred to as Beta 2+ for differentiation, but it’s 100% compatible with the original Beta 2, and you can still install the original Visual Studio 2005 Beta 2 on the new bits.
The only issue is making sure that you’ve got a Beta 2+ version of the .NET Framework on your machine if you want to install (for instance) the WinFX Runtime Components. If you’ve already got 50215.45 installed, simply uninstall it and install the new version (you needn’t uninstall Visual Studio 2005). The Beta 2+ version is included in the WinFX Runtime Components, so if you’re installing that on a bare machine, you’ve already got what you need.
To check which version you have installed, find %windir%\system32\mscoree.dll and check the Version tab under Properties.
Just to complete matters, Windows Vista Build 5219 (PDC build) ships with version 50215.562, but you shouldn’t ever need to touch that.