Posting From a External Form

I currently have a setup where I am receiving information on a daily basis. Now, I have some trusted people who I would like to allow to submit directly to WordPress WITHOUT giving them access to WordPress itself.

Is there a way that you can set up a custom form to post directly into WordPress? I’m assuming you would need to pass some custom variables for username, password, etc., but I really wanted to know if it is possible and if anyone has a plugin or sample code for that type of setup?

Thanks in Advance,

Brent