I think there's 2 different ways for you to meet admissions people:
a) You attend a pre-scheduled presentation on the program with other potential applicants (this could happen while visiting the school or at your home city for presentations "on the road").
b) You drop by at their office.
Scenario a) is advisable. Try to get as much info as you can from the programs beforehand and then during the presentation. Be prepared, ask questions AFTER researching their websites and other resources thoroughly. Don't just waste the opportunity by asking stuff that's in the brochures or websites. Ask for some specifics (eg: how to get in touch with alumni with careers like the one you are targetting, specifics about some clubs or activities, etc.).
Scenario b) I think is what Johnnyx is talking about. I also feel that dropping by without any other objective than introducing yourself and trying to be remembered could be counterproductive. However, if there's no scheduled event for you to attend, then you could try and set up an appointment ahead of time with a specific goal. This way, you would be showing respect for their time and they could always have the option to decline meeting with you, whereas if you dropped by they'd have no other option than face you (and they may even be irritated by your visit).
My case was atypical because I visited schools after applying and interviewing (and even after being admitted at one of them), so at the school where I had been admitted, I was invited by the adcom to "drop and say hi" while I was there. At the other 2 schools, I followed the rules, i.e. I scheduled the activities that could be scheduled via the website (such as class visits, lunch with students, program presentation, etc.) but did not seek any specific additional interaction.
Hope it helps. L.