What mic and input module are you using to record with? Any on-board mic in a computer won't work for this- it needs to be calibrated and accurate. You can use the computer as the source for the sweeps- look on teh left side and you'll see a generator. It has drop downs for Sine, Square, sawtooth, pink noise, white noise, etc. That would be your source, using the M-Audio, Tascam or whatever Input/Output device you decide on.
What is REW? I didn't see that anywhere on the basic version.