If you need to carry multiple VLANs across one port, then you need what is called a 'trunk port'. Where an 'access port' carries a single VLAN (unless you have a special circumstance of carrying a voice and data VLAN only), an trunk port carries multiple VLANs across the one link. Here is an example of how a trunk port is configured on a Cisco 3750 below. Go into config mode, and type out the two commands below the interface you want to configure a trunk port on.
interface FastEthernet1/0/47
switchport trunk encapsulation dot1q
switchport mode trunk
Some layer two switches will not take the 'switchport trunk encapsulation dot1q' command, so the latter command only will do just fine on those.
