It's very simple. You run the msconfig program, go to the startup tab, and then go down the list, one by one, typing in the names of programs you see there to Google or your search engine of choice. Read a few pages to get an idea about what the program does, and then decide if you want it running or not.
It'll be tedious and time consuming, but there is no central repository of info on this.
Currently there are many start-up programs on my system. I suspect some, perhaps many, of them could be disabled but I am unsure which ones they are.
Where can I find a listing that explains a little about what these many unfamiliar programs are and which I may disable without doing any damage to the start-up procedure.