512 MB would have been better but that would no longer qualify as a budget upgrade. Bottom line is, if your system has less than 128 MB of memory, you are going to see a substantial increase of performance simply by adding more. All mainboards featuring the Intel TX or VX chipset fall into this category. There are still enough of these systems out there which, in many ways are absolutely sufficient for almost everything. The second and probably more relevant bottleneck is the graphics adapter or video card.
Integrated graphics are, almost by definition, a low end solution.
They work, using united memory architecture, that is, they use system memory instead of dedicated graphics memory. If the integrated graphics adapter is used, a maximum of 30 fps can be achieved and for that, a Celeron 400 is sufficient. That means that any upgrade will have to be PCI-based. This may sound like an old fashioned interface, however, who has ever tried it, has experienced that the system performance was, at least doubled with the nice side effect of a much better image quality. In case one has one of the newer Intel i815-chipset based boards, the situation is actually much easier in that an AGP slot is there and any card can be used, including the highest performance cards like nVidia GeForce or ATI Radeon.