I have the following specs in a Win 98 PC:

P3 933 MHz
512MB RAM
Riva TNT 2
Voodoo 2 SLI
SoundBlaster AWE 64
64GB SD Card in SD to IDE converter

Normally I'm running 3D games via the Voodoo 2's at 1024x768. Under normal circumstances, everything works well (60+ FPS most of the time, except for the most taxing games), but when my NIC is enabled, I get frame rate drops (upwards of 15FPS in some cases, depending on the game geometry, texture fill, etc.). I've tried 3 different brands, and all 3 drop my frame rates in all games at that resolution. Of course, if I drop resolution, my performance remains above 60 FPS. I'm assuming that the CPU is being taxed heavily at 1024x768, but I thought at 933MHz, I'd have enough headway so as to not bottleneck the Voodoo cards if other background tasks are utilizing the CPU. The aforementioned NIC cards I've tried are a Realtek, Linksys, and 3Com. I specifically bought the 3Com to take advantage of its offload processing, and its ability to change configuration to a minimal CPU usage profile, but alas, the problem persists.

Of course, I can just disable the card in device manager when I'm not using it, and everything is fine. It's not like I need the PC on the network all the time. This issue is just an itch I have to scratch, and I thought I'd get an opinion here if this is normal behavior for the configuration I'm running. Is it normal for NIC cards in a PC of that era to be hitting the CPU hard enough to affect framerate at 1024x768 on a Voodoo 2 SLI config?