InterVLAN Routing and Multiple Switches

Not router on a stick. You got two vlans spanning two switches with layer 3 capabilities. Look at it as two vlans each with two routers physically attached to it...

Okay, let me make sure I'm clear... You're saying that the routing would be offloaded to the 3550 if someone on VLAN100 on the 4507R sent something to someone on VLAN900 on the 4507R? So it would go from person A on 100 to the interface they're plugged into, over the trunk link, get routed over to VLAN900 on the 3550, go back over the trunk link, into the 4507R again, and finally out the interface and to the destination? I guess the next question is, this happens automatically? How does the 4507R know to use the 3550 as a router on a stick? (Though I think I just answered my own question... the 3550 becomes a router on a stick as well as a switch that stuff can get plugged into... correct me if I'm wrong)...

Okay...I was wrong... the 4500 series aren't layer 3 by default. Once you assign an ip address to vlan 900 and vlan 100 on the 4507 and 3550 they should be able to reach each other without any additional routing because they are directly connected interfaces and your trunk between the two switch will switch the traffic.