|If you are using a wireless G card/adapter then your getting about the right speeds.|
54Mbps (Mega bits per second) is the rated speeds for wireless G.
If you calculate 2.25MBps (Mega Bytes per second), multiply it by 8, you get 18Mbps. Your actual throughput speed or transfer speed will be less than half of your rated speed. Signal degradation, policies/filters, RFI, qaulity of the networking equipment all play a part in performance.
If both PC's are wired and that wired connection is rated at 100Mbps then you should be getting around 12MBps on your transfers. If this is the case then you should check the quality of your cables, be sure they are atleast CAT5 and check for physical damage.
Turn off firewalls and see if that makes any difference.