^^ he has a socket 478 pin cpu which no g31/g41 mobos can support - so it's better if OP gets another 1GB ram around ~1.7k and remove and keep his one 512MB as backup module - thus he will have 1.5GB ram which is more than enough to run his office apps
BTW, his current 1GB ram is even enough to run office apps like office xp / 2003 and if he facing slowdowns in his system - first he should try optimizations apps like tune up / winxp manager / glary utilities etc. and see if can get speed boost and lastly he can try re-installing a fresh copy of Xp and all apps and see if his rig is performing better on those apps and only after that he should think about getting some new ram.