John,
I know your pain. I've had to take that off myself and its no easy job; especially for an old Eclipse. Obvisouly, make sure you don't disturb your timing. It can be a b&#$* to set on the DOHC Eclipse engines; plus you can ruin your valves and pistons if your timing slips.

I was able to break that free with a can of PB Blaster (the best penetrating oil I've ever used), a torch, a wet towel filled with ice, a breaker bar, and lots of swearing. I sprayed nearly the whole can of PB Blaster on it and waited a few hours. Then a torched it for a minute or so to burn off the excess penetrating oil and get that sucker nice and hot. Then I applied the wet towel with ice it to quickly cool it. Then I applied my breaker bar and torqued that sucker. It finally broke free.

That whole procedure may not be the best, but it worked for me. I can't guarantee it'll work for you. Be EXTREMELY careful with the torch; especially if you use all the penetrating oil. I had a small fire going for a few seconds. I hate using a torch on my car, and it's always a last resort for me. And if you just can't break it free, have a qualified mechanic do it. They'll have all the right tools, and they'll be able to set your timing just right. Though I usually don't recommend going to the Mitsu dealership for any repairs, this is a job I've had the dealership do... plus if they screw it up, they have to buy you a new engine :-D

Good luck!