Ya i just checked out your AP's web interface. I'm not sure that you can set a static ip for your router different than the other one that you have.
http://support.3com.com/infodeli/tools/wireless/accesspoint/3Com_AP8760_User-Guide.pdfMy suggestion now would be although its not the best when you want to manage one router just unplug the other one, which will allow you to manage the AP's separately.