The GT130 is just a rebadged 9x series card. Not sure which one, because at this point, Nvidia has rebadged the G92 cards 2-3x already, which is downright ridiculous.
Go with the 4850 though - it will be faster across the board, and in newer games, by a lot (plus, ATI writes better drivers for Mac OS X)
http://www.nvidia.com/object/geforce_m_series.html
There the 9600 GT and Nvidia GT 130 are in the same category.