Simple down to 3ms accuracy:
-- run query
On SQL Server 2008 and above you can use
SYSDATETIME() which has much greater accuracy.
You can also set a variable equal to the current time, run your query, and use
DATEDIFF to determine the delta in whatever granularity makes sense (however this won't work across batches).
SET STATISTICS TIME ON;
SET STATISTICS IO ON;
You can also look at the execution plans to determine where a specific query might have a bottleneck. I might recommend the free Plan Explorer for this (disclaimer: I work for SQL Sentry). If you generate actual plans from within the tool, it will show you actual runtime metrics for each query (everything shown above, without the work).