I think likely not.
Here is a handy chart of psu requirements:http://www.realhardtechx.com/index_archivos/Page362.htm
The 8800GTS is based on older technology and is more power hungry.
And... There are issues with dual cards like microstuttering,
Read this: http://www.tomshardware.com/reviews/radeon-geforce-stutter-crossfire,2995.html
If you want a graphics upgrade, I suggest you market your 430GT and replace it with a single faster card.
I would favor the 28nm based GTX6xx or amd 7xxx cards.
Your 550w psu will be able to handle a card as good as a GTX680 or 7970