I'm going to highly suggest not dating a co-worker....from personal experience...it's a really tough thing to do. You're always together...you have nothing to talk about because you are together inside and outside of the office...and you kind of just get sick of each other...but if you really feel like this could be something...here is how you can turn your flirtation into a relationship.

TESTING THE WATERS
It's a good idea to suss out whether your work  crush has the hots for you too. Some tip-offs: If he starts hanging around your  work space a lot or asks you to grab lunch or after-work drinks, says Stephanie  Losee, coauthor of Office Mate.

It's also promising if he's in an  unrelated department yet asks your opinion on a project of his — it indicates  that he is looking for an excuse to talk to you and values your opinion, notes  Losee.

You can do your own digging by jokingly saying, "Everyone thinks  we're seeing each other, ha-ha. Crazy, right?" If he casts a wide grin or seems  into the idea, the coast is clear to start flirting and see what  happens.

AVOID GETTING BUSTED
Once you've gotten together (we  know you'll get this thing moving), keep that info on the DL. "If it turns out  to be a two-week fling, nobody needs to know about it," says Helaine Olen,  coauthor of Office Mate. And monitor how often you bring him up. Olen says  coworkers often guess something is going on when one person mentions the other  too frequently. For example, "Here's that report...John helped with the  graphics" or "Where'd you go for lunch? Oh, John loves that place."

But  if you were chummy before, don't ignore him now — that draws more attention than  the occasional friendly moments does. No matter how covert you are, people are  likely to catch on, but there's no need to broadcast it.

WHEN TO COME  CLEAN
Most companies are lenient about dating (except between supervisors  and their subordinates), says Lois Frankel, PhD, author of Stop Sabotaging  Your Career. "They recognize its ubiquity." But there may be rules about  whom you have to inform and when.

If it gets serious (i.e., several  months), it's wise to tell your boss—even if you don't have to—before she hears  it from someone else, notes Frankel. Just say "I wanted to let you know Brad and  I are dating. We'll be sure not to let it interrupt our work."