You need to write code to retrieve the Outlook contacts. You can do this in C# using the Outlook Interop libraries. Given that this is a one-time task, I'm assuming, I would just use a Console application. Unless you are experienced with the Outlook Interop library you'll probably need to do some trial-and-error work. I usually find this is the case when writing against the Office libraries.
Examples can be found at:
Specifically about contacts: Get Outlook contacts into C# form-based application
Not specifically about contacts but when combined with the above answer should get you close to a start: Can I read an Outlook (2003/2007) PST file in C#?
Information on adding the Office Primary Interop Assembly that you'll need: http://msdn.microsoft.com/en-us/library/15s06t57.aspx