Treating furballs?

My cat Ming-Ming has recently started vomiting, this morning she coughed up a small furball, but then was sick again later. I've been giving her codliver oil, as i was told this would help to loosen the furball, but i dont think its helping. Does anyone else have any other suggestions?

I was given some Cat Lax(I think that's what its called) by the vet for hairballs. It really does work.

Pouring a teaspoon of extra virgin olive oil in with their food once every week or two helps.