Hey Frank,
Alberto and Vittorio really have some cool software, and the best part it's FREE! Try downloading SPECTRAN from their web site
www.weaksignals.org, it will allow you to dig signals out that are 20+ dB below what you can hear! It's the program of choice for LF DX.
Another great and extremely powerful program is Spectrum Laboratory by Wolfgang DL4YHF, very fancy spectral analysis program - you can define filters, derive I&Q channels, create a local oscillator and mixer and more. One application of it allows you to turn your PC soundcard into a vlf receiver!
http://people.freenet.de/dl4yhf/spectra1.html73 & HNY Warren K2ORS/WD2XGJ