Please point towards info for dummies (me).

One of my computers has on board video listed in manrake control center as
Description: SiS650/651/740 GUI 2D/3D Accelerator.
Module: Card:SiS 650
Media class: Display_VGA

1. Could my old monitor cause the above to not run at its best?

I know my graphics arent expected to be the best but I cant even run tux racer properly (extremly slow, to the point of not being useable)

My monitor is set at Generic 1024x768 @ 70 Hz.
Its a old Micron that they dont even confess to ever having made. (I cant find any monitors on thier website)

2. How would I find out if the driver mandrake is using for my graphics is working like it should? (should it be doing better?)

If the only thing for me to try is getting an updated driver from SiS I will but such things are still a little daunting for me.

<edit>
mandrake 9.2
2.2gig celeron
198 megs ram
asus p4s533mx mobo

Any advice much appreciated

It wouldn't slow the system down, just affect resolution and your eyesight. If Linux detected a monitor that could support 800x600 at 60 Hz 8 bit color it would not allow you to set your X above that, hurting your eyes, but not the speed of the machine. You need roughly 2K fps to run tuxracer smooth at 1024x768 @16 bit color. You aren't going to get that with the stock driver.
run glxgears, report what your fps is. At a guess, 300 fps is what you will get.
Note: with the stock nv driver on my GeForce 4, I got 277 fps freshly installed. Installed the nvidia driver, tweaked a little, back up to 7k fps with glxgears. The optimized driver makes all the difference.

The 650 family appears to have a Linux driver.

http://www.sis.com/support/drivermap.htm

RO