I have 1 template, and 45 categories. When I click on the link \"products\" which is my only category group, my side nav shows all of the categories parents and childs, which is
You should checkout this EE1/EE2 plugin which might do what you need:
GWcode Categories
http://devot-ee.com/add-ons/gwcode-categories
Examples of what you can do with the plugin are here:
http://gwcode.com/add-ons/gwcode-categories/examples
Available parameters and variables are here:
http://gwcode.com/add-ons/gwcode-categories/documentation