I configured my 3com 4500 50 port switch similar to the way Amaderog advised in post:
The only additional thing I had to do on my vlan 1 was to put a static route in my default gateway for my VLAN 1 clients to point the VLAN 1 clients to the 4500 for access to VLAN 2. The DHCP scop for VLAN 2 has the VLAN 2 IP on the 4500 as the gateway for those clients. Traffic is flowing between the two VLANs and each VLAN is obtaining proper IP addresses from the DHCP server.
I have two issues. First, on my DHCP server I use option 252 to pass the WPAD information for my clients to auto detect and configure their browsers. This does not appear to be passed over to VLAN 2 through the DHCP relaying on the 4500.
Secondly, although the VLAN 2 clients can reach VLAN 1 fine, they cannot pass any further. When I tracert from VLAN 2 to VLAN 1 clients I can see the route through the 4500 however if I try to tracert past VLAN 1, I get "destination unreachable" right away from the 4500 IP address.