Question : Wireless bandwidth is Lower than subscribed bandwidth

I've been trying to find an anser for this for a long time so I decided to try asking again on here.  I have Linksys WRT54G V5 54 Mbps wireless router.  I'm running XP Pro on all of my machines.  I have 5mbps cable internet.  When I do a speed test from one of my wired machines I get 5 Mbps.  When I run on from any of my wireless clients it always comes out around 2 Mbps.  When I do these tests I have all om my machines off except the one I'm testing.  I use 128bit wep and mac filtering.  I have tried the tests with neither of these running and recieve the same results.  I am testing this 2 feet from the router.  The wireless client states that connection is excellent 54 Mbps.  I transfered the same file between the same 2 computers inside my lan.  Once wired, a second time wireless.  The file was 550MB.  The wired transfer took right around a minute.  The wireless took a little bit over 6 minutes.  So my question is if the router does 54 Mbps and my internet bandwidth is 5 Mbps how can I get my wireless client to use it all??

Answer : Wireless bandwidth is Lower than subscribed bandwidth

Is the version/release of the driver the same under XP and Vista?  Could be a driver issue.  Do you have the most recent driver from the vendor for XP?