Rest assured, your music is SAFE. I personally know of over 60 people who have done this procedure so far.
Your music is in the \MY MUSIC\ITUNES\ folder. The Itunes program is in the \PROGRAM FILES\ITUNES\ folder. One has nothing to do with the other.
In fact, when Apple tells you there is a new update and you say YES, their software does and uninstall and then an install automatically. You are just doing the same thing but doing it manually.
Consider this. You can remove PowerPoint and MSWord from your computer and the presentations and documents you have on your computer are untouched. Removing software does not remove data files.
Your music, your playlist, your counts will be exactly as they were the moment before you downloaded 7.3.
It has worked for so many people. Get yourself back to the last solid working version (7.2) and life will be beautiful again.