I've moved this topic to the "Audacity 1.3.x / Windows" part of the forum (you can find the various forum sections from the index page
You should update to Audacity 1.3.12 as it contains some important bug fixes. You can download it from here: http://audacity.sourceforge.net/download/
If you previously installed Audacity into the default location you can upgrade by simply installing the new version over the top of the old one.
To record 2 tracks at the same time, you first need to ensure that Windows 7 is configured for 2 channel (stereo) recording.
Right click over the speaker icon in the System Tray > Recording Devices.
Right click on the recording device that corresponds to the Presonus USB interface.
In the "Properties", set the recording format to "16 bit 44100 Hz 2 channel Stereo (CD Quality)".
When that is set, open Audacity (restart Audacity if it was already open)
Go to "Edit menu > Preferences > Devices" and select the Presonus USB interface as the recording device and set the number of channels to "2 (stereo)".
When you record, the first audio input on the Presonus should record to the upper channel of the stereo pair and the 2nd input to the lower channel.
You can split the stereo pair by clicking on the name of the recorded track, and from the drop down menu, select "Split to Mono".