Hitting the brakes causes my headlights to dim.?

I noticed tonight that when I hit the brakes on my 97 sunfire, the headlights dim a bit. It's been an ungodly long time since my last tune up, but that is the same type of thing it was doing back then before I had that done. I know my rear brakes have some issues of their own (when they get wet, they bang when you hit the brakes. If you eek up on a stop sign, it's ok, but any real pressure at all and it's almost like they lock up, and then release when you hit the gas. Any ideas there would be GREATLY appreciated.) Any ideas what else it could be? I know the battery in the car is probably 5 years old too, so I am sure that that is not helping any. If you do know what it would be (i.e."You need a tune-up ASAP") Please let me know what all I need to do. i.e. replace your plugs and wires...

I'm not a car guy, but just like everybody else, money's tight and I am really just trying to keep it together for another year and a half until we need to replace it for other reasons!

Thanks SO much in advance!