Should I worry about commitment before I ask this girl out?

Sounds to me like you are "settling". I mean, you've know this girl for years and you haven't wanted to ask her out until now. I think you are correct in your umption that it is desperation. I don't think you need to think of commitment, but if you want to keep this girl as a friend if the dating doesn't go well, then don't ask you on a date. If, on the other hand you don't care (you said she's a distant friend), then ask her out. But, my opinion, you are really not into her as a girlfriend.