Do you have the EtherCD with 3Com DynamicAccess managed PC boot agent for your NIC?
That utility should do the job.
Enabling or Disabling the Boot ROM Setting
To enable or disable the NIC boot ROM setting:
1 Make sure that the NIC is installed and is connected to the network and that the NIC driver is installed.
2 Open the Windows Start menu.
3 Select Programs, and then 3Com NIC Utilities.
4 Click 3Com NIC Doctor. The 3Com NIC Diagnostics General screen appears.
5 Click the Configuration tab. The Configuration screen appears.
6 Under Network Parameter, select Boot PROM.
7 Open the Set Value list box and select Enabled to enable the boot ROM or Disabled to disable the boot ROM.
8 Click OK to save the setting and exit the program.