LAN: 100% U/L Speed, 15% D/L speed, intermittant packet loss

[Omega]

So here's the problem: From Computer A, I can upload at nearly full network capacity (80% of 100 mbps full duplex) to Computer B. From Computer A, I can only download at an average of about 15% network capacity. On Computer A, packet loss alternates between 0% and 4% (sometimes it will be entirely fine for hundreds of pings, and other times it will experience consistent 4% packet loss). Switching network cables does not solve this problem (both cables are pre-made cables, one is STP CAT-5, one is UTP CAT-5e).


I'm not sure if this is related, but I have a Gigabyte GA-7VRXP, with onboard Realtek LAN. I disabled this in the BIOS, but when I installed Windows, it detected my PCI D-Link 530-TX+ as the Realtek whatever. I updated the drivers for it, with the appropriate D-Link drivers, which Windows accepted without problem.


I kind of thought that somehow there might be some EMI along the cable run (of about 7 ft), so I've identified some possible causes, but it doesn't seem that any of them are the culprit.

The original cable run passes by (within 1 foot of device):
-Internet Gateway Router (NAT Device, power cable, 802.11b adapter, two UTP CAT 5 runs)
-Cable Modem (Modem, power cable, cable)
-Lamp (Lamp w/ 60W bulb, power cable)
-Alarm Clock (Clock w/ radio and speaker, power cable)
-Computer B with open side (Computer, cords, power cable)
-Surge Protector (Protector w/ 5 running devices)
-Subwoofer (Sub, audio cable, power cable)
-Laser Printer (Printer, cord, power cable)
-Surge Protector (Four devices)
-Into Computer A (passes by lots of assorted cables, power cable)

For the second test run, when I was troubleshooting the problem, I ran a cable that passes by (within 1 foot of device) only the following:
-Internet Gateway Router (NAT Device, power cable, 802.11b adapter, two UTP CAT 5 runs)
-Computer B with open side (Computer, cords, power cable)
-Into Computer A (passes by lots of assorted cables, power cable)


Here's an overview of my setup:
Computer A:
AMD XP 1900+
512 MB PC2700 DDR
Gigabyte GA-7VRXP
D-Link 530-TX+ PCI
Windows XP Professional SP1

Computer B:
AMD T-Bird 1 GHz
256 MB PC133 SDRAM
ASUS A7V
Netgear FA311 PCI
Windows XP Professional SP1

Switch:
Compex NP 16


I'd really like to figure this problem out, because transferring many GB at <2 MB/sec is fairly annoying.