Getting a list of site users in Sharepoint 2010

I'm developing an application on top of Sharepoint Foundation 2010. I'm wondering if it's possible to get all defined users of a certain Sharepoint site? By this I mean getting their IDs (or GUIDs, however they're represented) as we开发者_Python百科ll as their human friendly names. So I need any special rights to do this?

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SharePoint - Get a list of current users SharePoint - Get a list of current users