I used the crucial system tool to tell me exactly what type of ram i needed, it was brilliant, i just downloaded the program, ran it and it came up with how many slots i had for ram and how much the maximum ram i could put in it with all the details and all the options of what i could buy, the max my computer could take was an extra GB so I bought this in addition to my weasly 256MB and put it in. getting the case off my Sony Vaio proved to be a bit more challenging with the numerous spring loaded clips but i persisted and got it off. i slotted in the ram (Always seek professional help if you don't know what you're doing please - you can get electrocuted!) and put the PC back together, worked perfectly and computer is much quicker than before, i bought my ram for about £23 at the time but price do fluctuate, especially at the moment.
Has improved computer speed and reaction time, the real test will come when i have to use 3D studio max again for my multimedia assignment at uni, that is where my 256mb really struggled and kept crashing, hopefully now it wont, will update this if i remember to.