Hello Federico,
in latest configuration guide for 2950 in dot1x chapter it mentions the guest vlan
>>You can enable optional guest VLAN behavior by using the dot1x guest-vlan supplicant global configuration command.
This example shows how to enable VLAN 9 as an IEEE 802.1x guest VLAN on a port:
Switch(config)# interface fastethernet0/1
Switch(config-if)# dot1x guest-vlan 9
http://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_22_ea11x/configuration/guide/sw8021x.html#wp1025090
I'm not sure if this what you are looking for
Hope to help
Giuseppe