Why is my Internet download speed slower on desktop that laptop

Hi, Here's an interesting question about a problem that I have been trying to solve for a while - tried again over Xmas break.

Why is the Internet download speed on my Desktop (DT) so much slower than my laptops?

I have a 6yr old Dell Dimension 4550 running fully patched WinXP and two Acer laptops, one - LT1 (4 Yrs) with Win Vista and one - LT2 (1 Yr) with Win 7, both fully patched to latest versions.

My Internet is accessed through a BT Infinity connection (about 1 yr old) and the standard BT Router (version 3) and I am approx 500 yds from the fibre cabinet.

Since installation of BT Infinity I have never been able to get 'full' speed on the DT, but can achieve that on the LT's when they are connected by wire to the same router. For example...

- DT - LT1 - LT2 -
13MB 29MB 31MB - Wired connections to single router
13MB 23MB 28MB - DT Wired, LT's Wireless to single router

The figures are taken as an average from speed-tests run using a number(at least 5) of on-line internet speed test sites using the latest versions of IE, FF, Chrome & Opera.

Side note - no difference in speed was noticed prior to BT Infinity install as all PC's downloaded at around 6MB on previous broadband connection.

The latest Network drivers are installed on all machines, the latest firmware is installed on the Router, cables have been swapped, the router was swapped out and any other diagnostic half-splitting I can think off has been carried out.

To me I can only think that this is now a hardware issue in the DT, but what can it be? Should I go out an get a plug in network card (currently using the motherboard connection) or is it more fundamental in that MY DT is simply 'too old' to obtain a faster Internet connection than my Laptops?

I am all out of ideas and any suggestions on other areas to investigate would be most welcome.

I would check the nic speed for the desktop, to make sure it isn't statically set to 10Mbit. Also just check what the speed it's actually connecting at is. To check if it's statically set to something this may help.

http://www2.slac.stanford.edu/comp [...] _speed.htm

If you open up task manager and go to the networking tab ( I think this was still in xp) you can see what the connection is currently connected at.

I would think a 6 year old desktop should still be able to fully use a 30Mbit connection.