Operating system is Windows XP professional, Audacity 2.0.0 (unicode) downloaded from sourceforge.net. Sorry, I don’t understand the question regarding .exe installer vs. zip (yes, I’m a digital knuckle-dragger). Years ago, had an older version of Audacity, and was able to over dub (record multiple tracks) with an analog microphone. Now when I try to record a second track (even using headphones) the second track simply re-records the first track at a much higher volume. A friend has Audacity on his computer, and we are able to record multiple tracks using an analog microphone without the previous tracks being recorded again. By the way, the overdub on/off is checked. In the Audacity manual, it indicates that I would need a USB microphone in order to over dub, but my friend says I won’t be able to hear the first track while recording the second. Any help you can provide would be appreciated.

This tutorial from the manual should help you: http://manual.audacityteam.org/man/Tutorial_-_Recording_Multi-track_Overdubs