Hi, I read your post and I don't believe you can have one switchport assigned to two data Vlan's. You can allow multible Vlan's to cross a switch port with the "switchport trunk allowed vlan xxx" command.

here are some basic commands

config t

vlan 10

name test Vlan

adding the port

config t

int fa0/1

switchport access vlan 10

Have a read of the document below.

HTH

http://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_6_ea2c/configuration/guide/swgvlans.html

You can have a scenario like this.

Switch1 port 5 (vlan 10) is connected to switch2 port 6 (vlan 20)

There you have vlan 10 and vlan 20 under 1 switchport and they can ping eachother. This is not the proper way though.