I am rebuilding my calipers on my maxim 700 and would like to know how to get out a stuck piston. i used a grease gun on the caliper and one piston came right out. The piston on the other side is still in the assembly. It moved but the other one popped out first and released all the pressure.

you used a grease gun, i don't quite follow. so the caliper is full of grease?

put the other piston back in, but only part way. use a big c-clamp to hold it in place. then either use compressed air to try and drive the stuck one out, or connect it to your brake line and run fluid through, bleed the brakes then pump. you should be able to get that stuck piston out.
make sure to put a catch can underneath. brake fluid is nasty stuff

it's not a great idea, but if you're REALLY careful and can grab on with a pair of channel locks you may be able to pull and remove. but make darn sure you don't damage the piston. i'm sure others will disagree this this suggestion. i've never had to but may be a worst case scenario.

Well it came out. I used a grease gun becouse I did not hace any compressed air. It worked after I blocked off the other cylinder and was able to build pressure till the other piston came out.