HOW MANY WATTS lS NEEDED?

I'd say should be able to use a 400 Watt and be fine. Given the Motherboard is AGP it doesn't leave much room for upgrading, so most higher end Power Supplies that are designed for 2+ Graphics cards and monster processors would be nothing more than a waste of money. You may be able to use a lower rating supply, without further information in regards to if its a prebuilt computer or the components for a custom PC I can't say for sure.