The Compressor effect in Audacity 2.0 will help, as I said, and you’ll need to experiment with settings to get the sound you want.
I routinely use Steve’s Limiter effect Limiter to get an extra 3 - 6 dB of loudness from some of my vinyl rips.
Steve has also written an effect that implements the ReplayGain algorithm, which you can use to equalize the loudness of songs. ReplayGain plug-in
In both cases be sure to read through the whole thread to make sure you get the latest version of the effect, and learn how to use it (especially the ReplayGain effect).
– Bill