Range of wireless network

We have a network which is mainly hardwired with a few wireless NICs in laptops. We have 2 access points. The equipment is made by D-Link. The network is Win 2k server & win 2k pro. Within 10 feet of the access point the signal fluctuates widely between 60% & 80%. As the laptop is moved away the signal drops rapidly, losing it at about 45 feet, still with line of sight.
Is this ususal?
What range is ‘normal’?