a 1.6 GHz single core is in every way out of date for Divinity 2.
I had a 2.1 GHz dual-core with 2 MB RAM and a Geforce 8500GT. Very low-end. It was laggy on low graphical settings, with resolution 1440x900. Sadly running on Vista with only 2GB DDR RAM sucks too.
I put € 120.00 into an ATI 4870 and it's doable on high, very nice on medium now. I think with 4GB DDR3 RAM, I'd probably be able to play it smoothly on high.