ASP is currently at version 3.0 and chances are you are either using 2.0 or 3.0. And what version you are using depends specifically on what Web server you are using (IIS 4 uses ASP 2.0, IIS 5 uses ASP 3.0). So, what version of IIS are you using? That depends strictly on what operating system you're using! If you are using Windows NT Server then you are using IIS 4 (most likely, you could be using older versions of IIS... if you have a reasonably up-to-date Service Pack for NT, though, you're using IIS 4). If, on the other hand, you're using Windows 2000, you are using IIS 5. I promise.
So, to answer the question, "What version of ASP am I using?" more succinctly:
-- If you are using Windows 2000, you are using ASP 3.0 -- If you are using Windows NT Server (or Windows 9X through Personal Web Server (PWS)) then you are using ASP 2.0
(You can see a breakdown of what technologies are supported by what platforms in this article.)
Don't stress out, though, if you are using ASP 2.0. The differences between ASP 3.0 and ASP 2.0 are slight. For an article on ASP 3.0's new features check out: A Look at ASP 3.0. If you are really interested in the nitty-gritty, low-level changes between IIS 4 and IIS 5 (as well as ASP 2.0 and ASP 3.0), check out this Microsoft article: Leveraging ASP in IIS 5.0.