Well, I like the simple approach.. so why don't you just ask her to go and have a coffee (or another drink) after work? This might not be a real date, but it's the first step to asking her out on a real date and this might tell you a little more about how she feels about you.
I'd have a coffee with both a friend and a lover, so if you feel insecure or it turns out that during your coffee she seems not interested, you can still turn it into something positive. The way she looks at you tells you a lot.. does she look you in the eyes, what happens if you look her in the eyes? This will also give you an opportunity to talk a little, it might make her feel safer to go to such a place the first time than a party or a restaurant. If you are serious about her, then you need to take it slow anyway, she will let you know if she wants to take things faster
I'd do it now if I was you, there is no real reason in waiting for your 2 weeks notice. You can start by giving out simple hints that you like her (a little compliment), if she doesn't get it immediately, you'll have to be more direct. You can always ask her to go for a second coffee another day. If it turns out she is not interested, then just tell her that you wouldn't like this to jeopardize the relationship you have as co-workers and you will keep things professional and friendly.
Source: My co-worker and friend told me (after more than 10 years, I'm 31) that he is in love with me but didn't tell me as he didn't want to lose our friendship and I am in love with him too
I just wish he'd have told me sooner, that would have avoided a whole lot of problems. And I've always been able to work with him perfectly in the same department of our office, so that doesn't mean anything.