AGP Graphics Card Upgrade

[seacayenne]

I should like some advice as to whether I can make a worthwhile improvement in the performance of my set-up by just upgrading the AGP graphics card and which card should I go for ?
I've got a Radeon 9800XT at present. The cpu is Pentium P4 2.8ghz and the mobo is a Gigabyte 8KNXP .
The alternative would be a major upgrade to include new PSU, MoBo, CPU and graphics card (SLI/Crossfire ?) etc. I'd like to do this eventually but I need to delay until my finances have recovered. Maybe 12/18 months.

 

[seacayenne]

Additional info. on my enquiry.
Budget - £150-ish
1gb of memory
Space - O K.
My interest is at the moment mainly sims, flight & rail. But I've recently bought COH and a couple of other games which have made me feel I really do need to do something about improving my kit.

 

[seacayenne]

Many thanks for your advice. I think I'll hold fire until the funds permit the major upgrade.