How do you get the average response time for query a SQL 2005 server?
Response time for what? Opening a connection, executing a query, rolling back a transaction...?
You can get most information that you need from SQL Server Profiler traces so long as you have the appropriate permissions on the server. In addition to SQL Profiler there are dozens of performance monitor counters.
Your average response time for query execution is going to depend on a lot of things. Load on the server, size of your database, size and design of your tables and indexes, etc, all of which will change over time (sometimes even an extremely small amount of time).
Unfortunately there isn't a clear cut answer to your question. I'd highly recommend that you read through performance tuning articles and get familiar with SQL Profiler and the perfmon counters.