Why don't they just arrest Spitzer?

I'm told it's because impeachment can take months, so they'd like to resolve this . . . well, not amicably, but peacably, if they can. Still, if he's convicted of a felony, he will be impeached, and meanwhile, as soon as he goes to jail the Lieutenant Governor can step in with almost-as-good-as-permanent temporary powers. I don't see him having a lot of leverage.