Editing audio input real time

Is it possible to sample microphone input, modify it, and send it straight to the speakers?
I intend to make a program to modify sounds in similar ways to guitar effects boards.
Any indication of how to do this would be greatly appreciated.

I posted a recording class for DirectSound8 somewhere on here, in a thread where I guy wanted to do playback.. he posted the class he derived from my recorder, and between the two of them you should have no troubles accomplishing what you want

http://www.xtremevbtalk.com/showthread.php?t=242912&highlight=DSRec16Mono

Thanks for such a quick response!
It's a great resource there, and I will be look into it further in the morning.