Different speeds on different OSs and connection types

[#1]

Just a bit of a curiosity, really. I wonder if anyone can shed any light?
Much of my internet activity is done using a Dell X300 laptop set up to dual boot Windows XP and Linux Mint 8.
If I am in the lounge I use a wireless (802.11g) connection (about 12ft from the router)
If in the office (dining room) I use a 100Mb wired connection via an eternet switch (about 40ft fron the router)
Wireless is set up with WPA2 security and for the test only one PC (laptop OR desktop) was switched on at tme of test. There are no other wireless devices (PS3 Xbox etc) in the house.
Speed is better on a wired connection as you might expect but different results in different conditions are a bit strange.
Operating system           Wired (office)  Wireless (lounge)
--------------------------------------------------------------------------
Linux                                  13566              11147  (54Mb speed 88%signal)
Win XP                               12338              6598    (54Mb speed Excellent signal)
---------------------------------------------------------------------------
Upload speed is pretty constant 375-385kb/s
The PC in the office (wired connection and similar multi boot configuration (Win XP, Win7, Linux Mint 8 ) gave these results.
I plugged in a USB wireless adapter just to provide a comparison. It normally just has a wired connection.
Operating System               Wired             Wireless (USB adapter)
----------------------------------------------------------------------------------------------------------
Linux                                     13572             11022   (48Mb speed 82%signal)
Win XP                                  12444             6648     (54Mb speed Good signal)
Win 7 Pro                              13256             8266     (36Mb speed Good signal)
-----------------------------------------------------------------------------------------------------------
Tests were done within a few minutes of each other.
Not too worried about it as I don't use Windows all that much - just curious as to why Win XP is so slow on a wireless connection.
Any ideas most welcome - thanks in advance
Terry
[Moderator's note by Thomas (Be3G): space added to stop the forums incorrectly interpreting something as a smiley.]

[#2]

Is the MTU on the router set to 1500 - if not give that a go.

[#3]

The RWIN value on the Windows XP wireless connection might also be much too small, it needs to be 100000-150000.

[#4]

Different versions of LAN card drivers could produce the variance you report. Have you updated them all to the latest version? Rolled back the best performing ones to earlier versions to see if there is a corresponding decrease in performance?

[#5]

Thanks everyone for the replies.
@jelv - MTU in WinXP is 1500 and have set same on router (thomson 585v7) via Telnet.  No significant difference.
@spraxyt - That certainly helped XP - bumped RWIN up to 170000 and wireless download speed on the laptop went up to 10024 - MUCH better, cheers for that. The desktop machine in XP also responded well to this tweak - RWIN value of 120000 gave wireless d/l speed of 9224.  Increasing RWIN beyond these values started to reduce speed.
    Win 7, however, apparently does it dynamically so no change there. Fine on etherenet which is how it;s normally connected so not going to investigate any further.
@Ben Trimble - A ll drivers were latest versions at time of initial teting.  Tried installing appropriate Linksys XP drivers in 3 different versions in chronolgical order - no real difference except v2.33 would not connect at all.  Also tried generic Ralink driver (latest version) - marginal decrease in speed.
Sticking with the current Linksys driver and tweaking RWIN gave the best results.

Thanks for your input - an interesting experiment
Terry
Could not repeat this for the desktop machine as tI had to return it's borrowed USB adapter