Just read through your post again, do not hammer the fork! Pounding the fork with a hammer while it's clamped might do some damage to the tubes.

It should come apart with bare hands, just slam it apart. The only things you might damage when "slamming" are the teflon bushings, they are replaceable and cheap enough that you should consider doing them anyway. Also when heating keep in mind that its probably the teflon bushing that is stuck in the fork and not the seal, it's located just below the seal in the cast lower part so heat around there as well. Unless you use Oxy-Acetelene torch you will not easily damage the tube so if the heat does not work first time give it another go!