Well, you can sure search the ram with a "relative searcher" but there is not only 1 way to program a game so it's not said that you will find the decompressed text somewhere in the ram.
Anyway it's usually a good method with good chances of success.
As soon as you have the right place in the ram you can change the ram to see what happen on screen exactly how I explained in my post.
You can take a look at www.romhacking.net/start
and there should be at least 2 useful tutorials for your problem.
I will answer here for your other little problem.
If i am not wrong, there are some "standart" compression on the MD and you can find some tools online.
If they not work for you, you probably need to trace asm way the game to find the compression routine and then you have to reverse engenering it and build a personalized de-compression tool.