Please help, I think I have a clogged radiator.?

I came out of the store yesterday and noticed a wet spot under my van (1998 Plymouth Voyager) and noticed a drip from the radiator over fill area. I figured I had a leak. This morning I went out and opened the overfill tank and noticed it is COMPLETELY full. I opened the radiator cap and that is COMPLETELY full as well. I haven't refilled anything and don't know why it is over full. I already know i've needed a flush because the fluid looks rusty. Can anyone offer any suggestions.