jerky opengl, nvidia drivers

[zork]

To get accelerated OpenGL, i installed Nvidia's drivers
for my Geforce4 MX 440 on a FreeBSD 5.3-release machine.

The problem is, most of the games and apps that use OpenGL
do not run smoothly - every second or so they would freeze
for a little while which makes it impossible to enjoy them.

At first I thought my system could be too slow or something,
however, this also happens with simple apps, even screensavers.

What's more, the game Tuxracer runs smoothly without any problems,
and since it's a pretty fancy one, i guess that rules
out system performance.

Does anybody have a clue as to what could be causing this?