More information: It seems to be related to AGP texturing somehow, and specifically the texture sizes of player models and such.

For instance, on UT2004, if I lower the character detail so that the textures on the characters are irritatingly blocky, then it doesn't seem to happen. If I increase the character detail, I get hitches and sputters each time a character moves onto the screen from off the screen. It's as if it's having to reload the character's textures each time because it doesn't have enough texture memory on the card.

But I bought the card with the most texture memory (256). And I got an opportunity to try out an ATI card with 256 megs of texture memory, and it doesn't have this problem when plugged into my machine.

Besides considering an ATI card (which I am seriously considering at this point!) does anyone know of any driver settings that will improve the speed of these texture loads and prevent it from stopping the entire computer during the texture load?