Take off the swing arm, stand it on the engine mounting end and start soaking with kroil.
http://www.kanolabs.com/ If you have a 2001 and later bike your life is probably going to be easier and this is why.
More than likely you will be able to get the bolt free after soaking it with kroil for perhaps several days. However, if you do get it free you will probably want to cut the head off of the adjuster bolt with a dremel with a small wheel, cut a small slot in the bolt with the dremel or a hack saw blade and screw it through and let it drop into the swingarm. With the 01 and later swingarms you will have already popped the plugs to get the shock off and you can get the bolt out there.
The problem is, the bolt on the inside of the swingarm is probably really corroded. And if you get the bolt freed up and try and wind it out the regular way you are going to screw up the threads in the swingarm. And a heli coil adventure will be in your future.
At this point I'm not going to try and tell you about anti sieze. But, I will tell you a good way to help keep moisture out of the 01 and later swingarms. Drill a very small hole on the bottom of the swing arm down at the adjuster end, but, ahead of the solid section there. I have done that to both my 01 and 04 bikes and have eliminated the corrosion problem inside the swingarm.
You should be able to get the bolt freed up, so be patient.
Hope this helps,