3com wl-553 firmware - 3Com OfficeConnect Wireless Router

Usually the upgrade routine is in the router program. Log into the router and find the option to upgrade to latest firmware.

You can download the firmware from this WEB site.
http://webtopicture.com/download/download-3com-wl--firmware.html

You should be able to chain together. Only change IP scope on second unit to avoid any IP conflicts.

I had the same problem with the Ipod of my son.
To solve the problem, just upgrade your Firmware to the latest version. This will allow u to define the new MAC address. But the problem is that this firmware version doesn't work well, reseting the router every couple of hours. So to solve this problem, after you upgraded the FW and defined the MAC address, downgrade the firmware to you previous version, the new mac address will still there.
This workaround you need to do every time that you want to define any new MAC address

Please go to the router page and enter in to wireless security option. You will be able to see your password which you entered earlier.

Try to upgrade the firmware of your router.

There are actually 3 models of the WL-542. Go to this page and select "All downloads" in the section matching your model. You will find the exact model number on a sticker on the side or under your WL-542.

http://www.3com.com/products/en_US/searchbyproduct.jsp?search=3CRWDR100&sort=fname&searchby=sku

have you tried to Use PPoA?