Hello,
Microsoft has already released a Speech Recognition framework for you to use. It is called SAPI, Speech API.
"Microsoft Speech" http://www.microsoft.com/speech/
Where the newest SDK is called 'Microsoft Speech API 5.3'
For example, I have done a simple C# application that when I say "Volume Higher" it increases volume of the PC. I have interop the C++ Speech SDK libraries. Now I realized Microsoft created a Managed API which would make it even easier
It is easy to use, since your in Computer Science, it will be easy for you to understand the SDK in C++. Search for SAPI Tutorials on Google, and you will find alot of tutorials :) I bet you can setup a simple speech application in an hour or two.
Good Luck
======
Edit: Update:
Man, many people here make it seem so difficult to create speech recognition software. Dont' fall for that rumour, creating Speech Recognition is SO EASY if your using Speech SDK SAPI.
Sure creating a Speech Recognition engine is a lot of work, but why reinvent the wheel if Microsoft has a framework that does that for you? But since your trying to copy the voice from the Lecturer to Text, then you have to apply some filtering to that voice so it could be clear.
In University, for one of my labs, I need to control a robot, my teammates and I were bored that hour, so we applied the SAPI to the robot and with simple speech to text, we said MOVE, LEFT, RIGHT, MOVE, LEFT LEFT LEFT. Pretty straight forward.
That SDK allows you to train as well, so you can train your keywords.