i have an old computer Sempron 3100+/Nvidia GeForce FX5200, is it worth trying to mine btc on this old machine? I would be happy with 1 or 2 btc per week
I would say no, at the current difficulty the bitcoin calculator said that you would need 425MegaHash/second to get 2 bit coins a week, your card isn't on the list at
https://en.bitcoin.it/wiki/Mining_hardware_comparison so I don't think it's even compatible to mine with.