I gave a presentation when I was starting to show, and wore a black dress (think Ann Taylor style) with a white linen blazer. The black on the belly hid the belly, and the blazer drew attention away from it. It was not that I was trying to hide the pregnancy (nor are you, really), but just wasn't trying to emphasize it like some maternity dresses would. You wouldn't have known I was pregnant.
As far as telling, no, don't tell. If you are only 10 weeks, it's no one's business, that's for sure. People with fertility issues often don't tell for 16 or more weeks. I agree that you should wait until doing paperwork or even until starting. Of course, some future coworkers may snidely see it as deceitful, but that's none of their business. You just have to do your best to prove that you really want the job and are committed and will fulfill all of your obligations. Since you will be able to work until January, that's totally fair and true. I understand in the previous poster's case that she wouldn't be able to fulfill the obligations, so she would have to tell when the offer the job (and that makes sense too). Legally, they cannot discriminate against you, as you probably know.
Oh, and keep in mind that you won't be eligible for FMLA, probably won't have much sick or vacation time, so you will have to piece together any sort of maternity leave and will have to negotiate hard. Because of that, maybe it would be worth mentioning when they offer the job so that you can negotiate when you actually have some bargaining power -- if they don't give you what you want (you can ask for unpaid leave), then you don't have to take the job. If you wait until you have taken/started the job to tell, then they will have all the bargaining power around negotiating your maternity leave.
Good luck!
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