Slower speeds on wirelessly connected computer

[#1]

I upgraded to BBMax recently and have been getting approx 5-6 Mbps speeds on the computer that is connected to my router via the ethernet port. However, my husband's computer is connected via a wi-fi adapter and only seems to get about 2Mbps at most. Is this usual when connected wirelessly?
For info - the router is a Netgear DG834GT and the adaptor is the netgear one that compliments the router (can't recall the exact model number but capable of 108Mbps connection although we have it set to 54Mbps). The bathroom is between the room with the router and the room that houses my husband's computer.

[#2]

It is possible that the use of a USB WiFi adaptor is giving lower speeds than an cabled eithernet.
If possible try your husbands PC next to the router and check the speed there, if its the same then it is a limitation of the system. If speed increases then its the location.
I have known bathrooms to be constructed from foil lined plasterboard to prevent moisture damage, which plays havoc with WiFi coverage.
Chilly

[#3]

A further possibility is wi-fi channel interference.  When I checked using Netstumbler I discovered a weak signal from another device using the same auto-set channel (1) as my router.  Changing to channel 6 improved my link speed by over 10%, almost to the same as wired (my laptop has wi-fi built in).
There is also the possibility that tweaking RWIN and MTU might improve throughput.  This might apply on your main computer too, but only if (either) runs Windows XP (or earlier).  Windows Vista changes RWIN dynamically and will not benefit from RWIN tweaking.
If you would like help with tweaking RWIN and MTU please confirm which operating system(s) are used and post your router stats - sync speed, noise margin and attenuation from the router status pages.