If you go into Device Manager and look under Network adapters.
Look for the 802.11b entry and it may give additional details.
If not right click on it and choose properties. Then look under Driver for the driver details.
The problem may be the fact that the Wireless card is the old 801.11b which only has a maximum data throughput of 11Mbps which in realtity will be no greater than 5Mbps whilst the later 802.11g or n which you probably have in your other machines provides much higher and efficient throughput.