The thing with emulators, especially Nintendo 64 ones is that the programs is basically faking your computer to be that system, and I find the N64 ones are very hard to set up, as there are different video drivers your computer might work better with, and may need seperate downloads, as well as all those memory settings, etc.
I have quite a few emulators and do own the games I use, though the law states 24 hours is the limit if you don't, and then you have to delete. Or at least, this is how some websites save themselves from prosecution.
i think I have used that emulator though, and I don't think its one of the better ones.
Alot you see have many bugs, and you may find you've picked the wrong one for you.
Do a search, and I'm sure you'll find many good ones you can try out. Be careful though.