Inconsistent Speedtest results on 2 computers connected to net via same router?

I'm getting wildly different Speedtest results on two different computers. My main system is returning around 1.85Mbps, but another machine connected to the same modem returned 10Mbps (the speed I'm told by my cable company I'm supposed to be getting). The system is set up as follows:

Virgin Media 10Mb Cable Broadband Modem EO8CO13.00 ('Ambit')

Motorola Ethernet Router VT2442-VD (Vonage version)

Packard Bell Imedia with P4 processor, MS Win XP SP3, 1x80 and 1x40GB HDDs, 512MB RAM, aftermarket Netgear FA311 Network Adapter (main system, located in bedroom and connected via external Ethernet cable run and 2 socket faceplates to router in lounge)

Dell Optiplex GX150 with P3 processor, MS Win XP SP3, 40GB HDD, 512MB RAM (spare system, located in lounge, connected to modem via on-board Ethernet port).

Given that the only real physical variables seem to be the external Ethernet cable and the network adapters in each machine, I'm going to investigate the least potentially costly first (if it's a problem with the link cable, I can't work at height to replace it so would probably have to upgrade to Wi-fi at considerable expense). Bearing in mind I'm a complete novice where networking is concerned, any suggestions (and we really are talking a walkthrough here) would be very gratefully received.

I take it that the packard bell is the computer with the slower connection. How long is the cable that runs to the router? I've read that starting at about 100 meters the signal in an ethernet cable starts to degrade and that most certainly can contribute to your problem but it isn't necessarily the only factor. In addition if it is a low quality cable that could also effect performance especially if it is unshielded cable and somewhere along it's path you have some kind of electromagnetic interference such as from a speaker, tv, etc. Also to get the 10 mbps speed you need a modem capable of running that speed. From what I've read what might help is to have a ethernet hub or switch somewhere along the path. The simplest way to fix your problem, if you can't live with it, is to buy a wireless adapter and the only way if you don't want replace or modify the cable.

Hi townsbg and thanks for your response! You are correct about the Packard Bell; it's my main desktop system tucked away in the corner of my bedroom.

I'd heard the 100m limit thing on Cat 5 too, but in this case I don't think it's a cable length issue; there's about 5m in the bedroom to the faceplate, maybe another 5m or so clipped to the outside wall (it's only dropping one storey on the exterior of a brick-built Victorian house), then a 2m cable linking the lounge faceplate to the router.

So although it's quite a long run by some standards it's nowhere even approaching the 100m at which the speed should start to degrade. Also, the modem is brand new and Virgin Media assured me it had been set up for the 10Mbps; I certainly got it the other night on that creaky old Optiplex! That's what led me to question the network card and / or router, whether in terms of a fault or just settings that need to be changed.

Unfortunately whilst I'm not too bad on some aspects of computing (even to the point of building my own machines from cannibalised parts and installing OS's etc) home networking is something of a dark art to me and because of the variation between products there doesn't seem to be a straightforward online guide that's relevant to me.

I actually got a friend who's altogether more tech-savvy than I to link the machines so I could listen to the mp3s stored on the PB via the similarly ancient HP Omnibook that normally occupies the GX150's network connection in the lounge (and which despite its age and being on W98 also gives a reading of between 8 and 10Mbps on Speedtest!)