Let me start by saying I am a SQL novice. I have a test server that is running SQL 2000 and I would like to learn SQL 2005. Can I run them together on one server?
Yes you can have/install both on the same server. As you are saying that you already have SQL 2000 - is it a default instance? if so, you need to install SQL 2005 as a named instance.
Hope this helps and all the best for your learning.