Can I use 300W graphics card with 250W power supply?

I'm using an old motherboard and need a new AGP graphics card. The only one I can afford is a href="http://club-3d.nl/products/products_ending_page_7_with_id.cfm?product_id=156" rel="nofollow"http://club-3d.nl/products/products_endi…/a , but it wants 300W power. My dusty power supply unit says it's value is 250W. Can I still use the card? Do the missing 50W lower the card's performance or will it just not work?