With your system, I do not believe there would any real advantage to upgrading the motherboard.

The graphics interface (a general term for, AGP, PCI Express etc) and its affect on performance can be a little misunderstood. There is a tendency for people to believe the interface speed has direct relation to graphics performance. If this where the case, then the performance difference between AGP 4X (1.07 GB/s) and the AGP 8X (2.13 GB/s) would certainly account for a huge performance gap, but in reality, it makes so little difference to even high end graphics cards that it's hardly worth considering at all.

Every effort in developing graphics today goes into reducing the amount of work the CPU does on graphics, and maximizing the graphics' time share. This also has the affect of proportionately reducing the load of the interface between processor and the graphics card. Think of the graphics interface as a communications line; initially, the system puts as much information about what you're rendering on the graphics card's local memory (that's the 256 MB part of the name). This occurs during the loading phase of an application (and sometimes later, but lets not make this complicated!). After that, instructions pass from the processor to the graphics card in an abstract way, telling the graphics card how to construct and manipulate the rendered scene, and the graphics controller (that's the Radeon 9550 part) does all the grunt work. If you imagine then that these instructions are consumed by the graphics controller as quickly as possible, the stress on the graphics interface is somewhat proportional to the performance of the graphics core.

It's hard to directly compare graphics card performance, but to put things in perspective, the Radeon 9550 Core (code name RV360) is a low end, last generation product that is capable of outputting around 1 Gigapixel/s. By contrast, the the Radeon X850 XT PE (code name R481) could produce over 8.5 Gigapixel/s. Current generation products for AGP will exceed even the R481's performance. I would be prepared to say that AGP 4X would probably be a little tight for the latter, but perfect sufficient for the former.


As for RAM, you could benefit from improved memory bandwidth, however to guarantee any sort of perceivable performance increase you would have to buy a motherboard of decent quality that supports dual channel, but it would seem that you do have some budget constaints. This is mainly due to the fact that the Celeron 2.6 GHz has certain limitations that prevent it from capitalizing on memory bandwidth.


All in all, I would recommend you stick with what you have until you can't take it any more, save a bit of cash and buy something decent from the get-go.