You could install a "faster memory" memory IE PC100/133 but make sure you put this in the first slot and if you can try and get the same make as the memory you already have installed.

In previous post people have said that hdd size and memory are not related whilst this is true from a hardware point of view it is not strictly true from an O/S point of view.

Windows will take a portion of your HDD and use it as Virtual Memory by default, if you have a small hdd it means that it cant take as much, in low spec systems this can slow them down a bit, so if you do get a bigger hdd but keep what memory you have windows will be able to use more hdd space as virtual memory hence increasing preformance!