Like Farrah, I too work in an office environment where I have witnessed some pretty insulting things. Especially working at a law firm, you really see things under a microscopic view.
One of our Taxation Attorney's, Jim, was having a lurid affair with this trampy harlot named Marchelle. Which I have ranted about forever in the Rant and Rave thread lol. Marchelle wasn't even a paralegal but a mere secretary and both parties were married! She also worked beside him catering to his every whim and call along with pursuing him. The whole office had to suffer the dramatics of their relationship, especially if they were fighting.
I personally think its a bad idea because of what I've witnessed with Marchelle and Jim. They made it so obvious they were guilty by always 'sneaking around' or she was constantly in his back office, never at her desk. It aggravated the staff especially those who were competent enough to do their work. I felt rather frustrated because here I was busting my ass and these two were getting a free ride. Neither of the firm's two partners acknowledged the affair or spoke of it. Which, I always thought was ridiculous, they should have both been fired. Co-workers can also gossip about you, including men, which Farrah mentioned.
I'm getting off topic but like Rampage said it also varies with each position in the job. If you see this person frequently on a daily basis that might be a bad idea. BUT, if you see him less frequently than that might be better.
I guess it really depends on how much you like him. You have to ask yourself if its just a crush or the blossoming idea of an infatuation or more? The simple approach though is good, especially if you two have things in common. If your working on an assignment together that's an open window. Maybe try asking him out for dinner, coffee, or even a drink. If you want to lesson the nervousness gather a group of friends with you whether from work or your circle of friends.