Eh, you need the codeword from the shop owner up front. Ask him if there's "noting more exciting" here (or something along those lines). Only works with low karma and / or high speech skill.
Just a gamble table behind it, though, and it seems awfully rigged too
If I remember correctly, you need a decent gambling skill to be able to enter that building. And you'll have to pay to get the password from the guy in front of the building.
Hm. I think I usually take some Psycho or Buffout, and I use a crowbar to open the door instead.