well its pretty obviously that it would increase your system performace..since adding more ram causes less swapping to the Hard drive.
1GB is fine and even good,2GB is perfect.
My System:
CPU : AMD "Barton" 2500+.
Memory : 768MB DDR PC2100.
GFX : Nvidia 6600GT DDR3 128MB , AGPx8
M\B: Gigabyte GA-7VT600P-RZ MotherBoard
Sound: AC97 Realteck 5.1 ALC655 - Audio.
