Range Extender Password

Hey Guys,

I recently purchased the Hawking 300-N Range Extender to get my wireless signal into a guesthouse on our property. I set it up using the CD setup, and everything seems to work great. I am using a D-link DIR-655 Router as my main router, and extending the signal from this.
There is a password on this extender, a rather long string of numbers & letters (same as on the router) that I don't want to have our guests enter every time they want to use the internet wirelessly. My question is this: can I have different passwords for each? Can I leave the router password-protected and open up the extender with no password (or just a simpler one)? When I set it up, it just automatically set the extender's password as the same as the router's password. I want to allow those using the extender to have easier access, and keep our router in the house protected.
Is there a way to do this? Also, how will this be security-wise for us - will opening up the extender allow whoever uses it to access our shared files that would be accessible through the router?

Thanks for any help you can offer.

Frank