Banks hire agents to market the properties for them and to present offers to the bank. If you call the agent who has the listing, I'm not sure if your state has what's called "dual agency" - where an agent represents both the buyer and the seller. While some states permit this, others don't. If the state doesn't permit dual agency under license law, you could contact another agent and have that agent show the house. It's really up to you; just be sure you understand who is representing whom so you know your rights in the homebuying process. Nice that you're looking to buy your first home! I remember mine... it was so nice to go in and say "hey! Neighbors can't hear us singing or laughing - excellent!" =)
As to new construction, builders are in a bind somewhat since the market went kerflooey - an agent can check to see how often or if the price has been reduced and the agent should be able to let you know how your offer price stacks up as to actually getting to go through the process of purchasing the home. It's a bit of a tricky thing, negotiating, particularly if lots of homes have been on the market for a year. That said, a good agent will have good to great negotiating skills, and protect your interests as well.
Good luck and here's good thoughts coming your way!
Gina Kay Landis
ginakay DOT landis AT realliving DOT com
Follow me on Twitter: @ginakay