the gpu i would go for a radeon hd 7750 low profile version, for that one you need about 350W-400W psu, but beware that you need a small psu to replace your current one
ram would be hard to find as you need ddr2 i think, but ok, maybe it would work without it too...
my suggestion would be to get the graphics card, if the 240W psu is a good quality one it might just work with just that, the gpu needs at max 75W of power.