Dell just released a new BIOS update for the Dell Optiplex 755 system, version A13. This update includes an AMT firmware update to version 3.2.3 also that resolves a couple of security issues. I just performed the update on an Optiplex 755 that I had already provisioned, and it didn't break anything 
If you're deploying the BIOS update via a ESM software package, such as Microsoft System Center Configuration Manager (SCCM) 2007, you can automate the staging of the BIOS update (without forcing a reboot) using the following command line:
O755-A13.exe -noreboot -nopause
Trevor Sullivan
Systems Engineer
OfficeMax Corporation