Lockups with network traffic

[Guest_imported]

Here's the deal... I've got a rig that has been rock solid stable in win9x (98se and ME). No change in hardware, only the OS has changed. Upgraded to Win2k pro and I am having the following issue: I am subject to sporadic lockups whenever there is any network traffic involved. In my home there are currently a few 98se and winME machines along with this machine behind a linksys router through to a cablemodem. The boxes are all getting DHCP'd through the router which is of course providing NAT Service. I'm getting lockups whether I browse through Internet Explorer as well as when using just mIRC and I've had the lockup in Outlook as well while sending/receiving. I've had this problem on two completely seperate installs (os progression: 98se->win2k->98se->WinME->win2k). I'm running with SP1 and ie5.5sp1. So far as I can tell it is one of two things, though I believe I'm only left with one. During installation, it gave an error and halted telling me my bios wasn't fully acpi compliant. As a result I've been using a non-acpi HAL. I flashed my bios, reenabled all the power management functions and reinstalled as an upgrade on top of itself. This time it went through fine and is using an ACPI HAL. However, it is still giving me the same lockups. The only difference is that with the non-acpi hal I could press the power button to turn it off when it locked and now I have to hold it in for 5-6 secs (of course) to turn it off. The only other thing I can think of is the network card drivers. I'm using a 3com 3c905b NIC and have updated to the latest drivers I could find on their site (terrible knowledge base). Still locking up. Tried disabling busmastering for the NIC per one of the Technet articles. I have updated all the drivers for all of my hardware as best as possible. I thought I had the same problem in Win98se but I updated the sound drivers and it was fine. No luck here. Symptoms: Sporadic hard lock. No errors, no blue screens (haven't had one yet actually). If I was clicking on a menu at the time, it will actually freeze during the "fade in". In mIRC, right before it locks the mouse will start fading out of sight. In IE, the mouse is visible when it locks.

My system:
Sparkle 350W PS
Gigabyte GA71XE mbd (amd 751/756) - bios rev f3 & f7
0.18 micron Athlon classic 700
Guillemot Geforce 256 (3d prophet) - 6.31 ref drivers
Sound Blaster Live!
3com 3C905B NIC
Maxtor 20gb 7200 rpm ide hdd with udma66 cable
Kenwood 52x ide cd-rom
Plextor 8x4x32 ide cd-rw
MS Intellimouse with intellieye
7 year old AT keyboard with ps2 adapter

All patches/driver updates installed that I could hope to think of.

It will be very sad if I have to go back to a consumer grade OS for stability. Thanks in advance for any help you can give.