Configuring ethernet port failover in Windows 2008

I have a Dell R300 server with two ethernet ports, running Windows Server 2008. I'd like to use one IP address, and connect to two switches. I only need one port at a time, I don't need more speed. The idea is, if one switch or one ethernet port goes bad, traffic continues on the other.

I had something like this set up with "bridging" the ports, and assigning an IP address to the bridge, but this had unintended consequences. When the network topology was reconfigured, the switches suddenly stopped switching traffic between each other. After much troubleshooting and resetting the switches to default configuration, the R300 server was tracked down as the culprit. With even only one ethernet port plugged to one switch, the switches would stop talking. Removing the bridging mode on the R300 (or unplugging it) solved the problem. So, whatever solution is provided, I'd like it to avoid this switching problem.