PTR? How? And Question.
 

Exactly how does using the PTR work? I went to download the client, and I wasn't exactly sure I liked the way the file name was...would turn my 2.0.12 client to a 0.1.0 client? Eh?

One question: Any other MMO I've played that has some kind of test server, I was able to separate test server files from live server files, so that I could play one or the other, and not have to repatch back and forth all the time. Is it possible to do this here?

When you install the PTR client software, it creates a subfolder under your primary WoW folder for all files relating to it.

You run the WoW.exe from under that folder in order to log in to the PTR.

I am not sure, however, how it separates any addons that you might want to try out, use, etc. The last time I had played on the PTR, I don't recall if there was an "Interface/Addons" folder or not under the PTR folder.

Yes, in your WoW folder it creates a WoWTest folder (which is like a copy of your wow folder, but with ptr related files). In your WoWTest folder, you may copy over your Interface and WTF folders, though keep in mind that some addons needed to be changed to work with 2.1 and also that you may lose some profile settings for addons since you'd be playing on a different server with a different character name.

The version number is the patch revision number. After downloading the PTR client, you'll need to do about 6 (don't remember how many now) updates to get to the current patch revision. Also think if you want to get on the PTR this late in the game - you'd have to do all those updates and I think the PTR may only be up for another day or two. The most recent patch to the PTR seemed like it might be the last..... But these are just my predictions - I'm not 100% sure of when the PTR will go down or when 2.1 is coming.