I was changing my rear pads, and one of my rear calipers has seazed on it's bushing. the one it slides back and forth on. I'm not sure if this means the whole caliper is ruined. can I replace just the bushing and the rod it slides on?

 

The caliper seized on the slide pin? thats really not good. If you can get the caliper off of the bracket you might be able to clean up and replace that bushing. but, if the caliper is that corroded, you would be better of just replacing it. Because, whos knows what it looks like on the inside.

I had a similar experience with a rear end i bought. One of the calipers was locked up like you described, and had to be cut off the bracket with a grinder.

Try unbolting the caliper and bracket off of the axel housing. if you dont have a way to cut it, i would imagine that any machine shop could cut it off for you.