Range extender dropping connections & IP conflics

I hope the Tom's Hardware community can help this tech/network novice fix trouble with a new office network setup.

We just upgraded internet service to Comcast Business and updated network routers to accommodate a new office layout - unfortunately, we have been experiencing problems with IP address conflicts since the upgrade:
every time a sleeping laptop/handheld is waking up from sleep, we see error messages about conflicting IP addresses or the computer will time out trying to connect to any of the wireless networks.

Since we were not able to run Ethernet to all new office spaces, we added a Belkin range extender to "bridge the gap", so I am suspecting this is somehow creating the IP conflicts ...

Office set up is as follows:

Internet (Comcast Business ) >> Motorola Modem & Router (SBG6580) >> WIFI >> various laptops/smart phones & Belkin Range Extender (F9K1106)


Belkin Range Extender:
>> WIFI >> various laptops, iPods, smart phones
>> ETHERNET (via splitter) >> AppleTV, GoogleTV &TimeCapsule/AirportExpress - both in router mode: Off (Bridge Mode)

Reading through other forum posts, it sounds like we may have to set up static IP addresses for each machine?
Question: how do you set up those IP Addresses (& where do you find out the address numbers to use)? And would they need to be set up in Motorola modem or Belkin range extender?