Its best to make sure that your computer is connecting at the full speed supported, 54Mbps I am assuming.
Are you using WEP?
WEP often times will slow down the transmission rates of data, normally it isnt noticable, but sometimes there are faulty firmware issues that can be correctly by firmware updates.
Which then leads me to firmware updates, It is possible that there is a flaw is the firmware for your router, your should probably check and make sure that you have the latest firmware for your device.
The MTU
The maximum transmission units. This is normally set to 1500, I have noticed that even 1499 makes a huge difference on my network, so just make sure that is set right.
Are there any enhanced capabilities?
Many companys try to best sales of specific products by claiming that they are capable of a Super G Mode with packetbursting or etc... Try using these enhances and see if they actually perform well, but if they dont do anything at all, it is best to disable, for they may give your problems in the future.
Last but not least, your service provider.
Some of these guys just blow, they claim that you will get I dont know lets say 3Mbps downstream, but in reality you only get 1.5 or something. That just happens, the best way to check on this is to do a
speed test, this will let you know where you sit.
I have been rather breif about this, and sorry for any type-o's