So an Apple genius was telling me I can use an AirPort Express as a wireless extender to the Airport Extreme, is this true?
I bought both, I think he was wrong but perhaps you guys know better then me.
Yes, the Genius is correct, you can use the AE as an extender for the AEBS.
AEBS (AirPort Extreme Base Station) AE (AirPort Express)
When using the Mac's built in AirPort Utility under manual setup for the AEBS click on the AirPort Icon > Wireless tab and it will have a box that says "Allow this network to be extended". Make sure it is checked. Click on update to save the changes and the AEBS will restart. Then, verify that the box is checked after restart.
On the AE using the Mac's built in AirPort Utility under manual setup: AirPort Icon > Wireless in the drop down box choose "Extend a wireless network". Then make sure to pick the SSID of the AEBS, enter the password and make sure you have the proper (matching) encryption level set.