First, make sure you have both the vlnvidia package and the kernel sources installed.
If not, you can install vlnvidia using gslapt, and the kernel sources by downloading this package:http://vectorlinux.osuosl.org/veclinux-5.9/packages/kernel/kernel-src-188.8.131.52-i586-1vl59.tlz
(do installpkg to install it)
After that, running "vxconf" as root (or navigating to the X configuration in "vasm) should get you to the dialogue that allows you to install the nvidia drivers.
If you're in a graphical environment, you should do that after running "init 2" (as root) to take you to textmode.
You should probably choose "Expert install" when it asks you about the nvidia drivers and choose the right version.
I'm guessing the latest version wouldn't support the Geforce2, so you might have to take a look at the supported cards for the different versions in the nvidia website.
Or you can just go with whatever vxconf chooses for you: it might get it right.