Thanks for all the responses TT4U and cdogg - nice to know someone out there cares.
I've been having a look at the device enum in the registry and it appears that the registry thinks it has things right by installing the PCI to PCI bridge etc..
I know it has it wrong !!!!!!!!! So I tried a wacky idea !
I had a look at the Intel INF file that installed the correct drivers for XP and noticed the only real difference was that the signature of the file refered to $WINDOWS NT$ in the XP Version and $CHICAGO$ in the 98SE version. Both files are named 865.INF. So like a mad fool I re-hashed the INF file for XP and changed the signature to $CHICAGO$ - when I ran that through the system it found two new devices called 'INTEL 82875P Processor to AGP Controller' and 'Intel 82875P/E7210 Memory Controller Hub' -I thought I'd cracked it until I rebooted and found that even though the devices are now present in device manager with no strange effects on the system, the AGP 8X still does not work and Sandra Pro and DX Diag tells me the AGP is disabled.
I've now been through all the devices listed by connection in device manager and updated them all via the web - many that were Microsoft drivers have now changed to Intel ICH drivers. Strange, but I have a feeling that if I had maybe done that in the first place it may have worked. The next plan of action is to have a go at a re-install of 98 as suggested on another HDD but before I attempt to install the 875P chipset drivers I will do an update via the web on all - and I mean all - the devices listed. I'll mention that when I did the last install I only installed 98SE - I didn't install the dual boot. Can't thanks you folks enough for all the valuable Info you have passed on. I'll let you know how things go.
Gigabyte GA8KNXP MoBo - P4 Prescott 3.0G CPU - 512 Corsair (256x2) Matched Pair DDR - 4 x HDD (360GB) - TI4800 8X AGP - 2 X CDRW - 1 X DVD - 550W PSU - Dual Boot system XP Pro & WIN98SE