Looking up Congressional Hearings is a bit tricky. Here are some tips.
You can look up Congressional Hearings using Lexis-Nexis Congressional: http://web.lexis-nexis.com/congcomp.
In Lexis-Nexis t's is helpful to use the Advanced Search feature and to use limits.
You can limit a search to hearings only, which will greatly reduce the number of hits.
If you are looking for testimony by a particular witness, you can limit a search to just witnesses (i.e. Oliver North).
You can limit by years, including limiting to a span of years, (i.e. 1950-1955).
If you know which Congress held a particular hearing, you can limit a search to just that Congress (i.e. the 95th Congress which met from 1977 to 1978).
When you find a citation to a particular hearing, click "Go to Full Text" to see the actual transcript of the hearing.
Here is a handy guide to Congressional Hearings: http://lawschool.lexis.com/infopro/zimmerman/disp.aspx?z=1324