Freelancing in Malaysia with work visa

Hi all
I have a work visa and am currently looking at also doing some freelance work:
- one lot for the company that got my visa but a different category of work
- another lot for another company
Does anyone know if this is legally possible? And how do I figure out the tax I need to pay?

If you can recommend anyone who can advise on the tax, that would also be great.

Your help is much appreciated!

Unfortunately unless you are self employed in your own company, freelancing is rather difficult for the reasons you state. An employment visa is only valid for the company in which you work.