First i must apologise for mentioning the wrong model number for my motherboard. My motherboard is a ASUS A7V8X with the VIA KT400 Chipset. For your information Asus do have a A7N8X which is based on a nForce 2 chipset and its also shown on their website.
I am using the drivers give by Asus and revision is v31.40F. AGP aperture size is set at 32 mb. I don't quite follow what AGP aperture size means. My card is a 128 MB card but my understanding of that setting is whether to use System Memory for AGP requirements which is why i have kept it at a minimum. In fact i shall give you all the info which i have manually set in the BIOS cause the default seting of the BIOS also gave the same problem. These settings i have made have not changed anything as far as stability goes. I cannot find an AGP Drive Strength or Video Bios Shadow option on this motherboard bios though i remember seeing it on other models. Memory Frequency Setting is at 333 Mhz, AGP Capability at 4X, AGP Fast Write ENABLED and Primary VGA Bios on AGP VGA CARD. My memory is registered and the model number is Kingston Value RAM KVR333X64C25/512. Thanks very much for your help and looking forward to your reply.