Flickering huh? OK let's see if I can help...
There are usually 2 different flicker effects - one appears like the screen goes blank for an instant; the other appears as the image jiggling up and down - I'm assuming from your description it's the former.
Since you're running XP, try this: 1) Right-click on your desktop; 2) Choose Properties; 3) On the Display Properties window, choose Settings then Advanced; 4) Choose the Monitor Tab; 5) Below the drop down Screen refresh rate menu is a box with the phrase ` Hide Modes That This Monitor Cannot Display '. Check that box (or leave it if it's already checked; if the box is grayed out, then go to no.6); 6) Go to the Screen Refresh Rate List and choose the highest refresh rate offered. 7) Choose OK then OK again; 8) Restart the computer and see the difference.
If the problem isn't resolved, then the flicker problem is the latter. In that case, go back to Display Properties> Settings. Check the screen resolution area and move the slider one position to the left. Click OK then restart your computer.
If the flickering still won't resolve you may need to replace either your graphics card, your monitor or both.
Whew I said a mouthful; hope this helps