I have this cancer spot on the car: http://s55.photobucket.com/albums/g149/frogedude/?action=view&current=HPIM16852.jpg. I know it was from water leaking in through the window. I am going to seal up the window. I was down at the auto part store and seen several different types of bondo. What type of bondo would you recommend or should I use fiberglass?

If you want to fix it right, you should take out the window and strip it down to bare metal. So there is NOOOOOO rust. Bubbling paint like that can hide some pretty bad stuff. I wouldn't even think about what kind of filler you'd use until you know exactly what is under there. If you bondo over ANY rust, it's gonna come back on you within 6 months. If that's all there is on your car it shouldn't be too big of a problem. Just fix it right. You gotta get rid of the rust 100% and assess the integrity of the metal underneath. Is there just a little pitting or is there rust going all the way through. If you find just some pitting and the metal is otherwise solid. I'd wire brush it, use some navel jelly. Put some epoxy primer on it, then filler of your choice. Bondo brand would be entirely fine for fixing a little surface pitting.
That rust looks pretty nasty though. The metal might be in bad shape.

grind the hell out of it and then use rage gold body filler

DONT USE THE STUFF AT TEH AUTO PARTS STORE!!

NEVER USE FILLER OVER RUST !!! it will come back 10 times worse, cut out the rusted area to about a 1/2" arround the rusted area.Weld in new metal easy fix. Finish to perfection and no more rust problems :hurray:

The rusty areas will need to be cut out and replaced with sheet metal. Applying any type of filler over rust is only be a temporary fix. You'll be amazed at how much damage has already been done. What you see is only the tip of the iceberg.

Tom

NEVER USE FILLER OVER RUST !!! it will come back 10 times worse, cut out the rusted area to about a 1/2" arround the rusted area.Weld in new metal easy fix. Finish to perfection and no more rust problems :hurray:

I agree, if you just cover it up with bondo you will be sorry you did it. Check it good ,see how much rust is there, cut it out and replace with good metal . The extra time put in will be worth it in the long run.