If you haven't already gotten them, you can find the BIOS files here:
http://www.emuparadise.org/biosfiles/bios.html
The way to "work" these BIOS files is to extract them to the correct folder. Which folder is the correct one varies with each emulator. Read the help files and readme.txt files that usually come with each emulator to find out what to do.
Also you might want to check out this site for further help:
http://www.mameworld.net/easyemu/