popcorn...you are scared of rejection because you are insecure about who you are, simple as that. you must overcome this. u r 24, it's time to step up and be a man. if u don't pretty soon, it's unlikely you ever will.
ask her (or any chick) out as if they are your "friend", but do NOT act as though u want to be their friend, as per this whole site. afterall, u r getting to know this person merely to see if you have chemistry (attraction).
let it fly and have fun. if it helps, don't consider it a "date" per se. that'll take the pressure off.
practice asking her out in front of the mirror. get your general "lines" straight and repeat over and over and over. have a line if she accepts, a line if she's wishy washy, and a line if she declines.
ask her in person, but NOT in front of anyone else if you can muster it. wvssy pvssy boyz ask via email, although i've done it when appropriate.
good luck bro...