Here is a link to the Configuration guide for 12.1.11 code:
http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/12111ea1/3550scg/index.htm
It may be easier to think of the 3550 as a router with many Ethernet interfaces if you're trying to do L3 stuff. All ports are shutdown by default.
Here is a sample config:
version 12.1
no service pad
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname switch
!
!
ip subnet-zero
!
!
spanning-tree extend system-id
!
!
!
interface FastEthernet0/1
no ip address
!
interface FastEthernet0/2
description Routed port
ip address 172.16.1.1 255.255.255.0
no switchport
!
interface FastEthernet0/3
no ip address
!
interface FastEthernet0/4
no ip address
!
interface FastEthernet0/5
no ip address
!
interface FastEthernet0/6
switchport trunk encapsulation isl
switchport mode trunk
no ip address
duplex half
speed 100
!
interface FastEthernet0/7
no ip address
!
interface FastEthernet0/8
no ip address
!
interface FastEthernet0/9
switchport access vlan 11
switchport mode access
no ip address
duplex full
speed 100
(rest of interfaces snipped for brevity)
interface Vlan11
ip address 192.168.1.1 255.255.255.0
!
ip classless
no ip http server
!
!
!
!
line con 0
line vty 5 15
!
end
