To be sure of getting decent performance in The Sims 2 I would go for the Vostro 1500 with a dedicated graphics card. I am pretty sure the 128MB nVidia GeForce 8400M GS will be sufficient.
You can find the minimum computer system requirements here:
TheSims2.com - Help - Detail
Also if you decide to go with Windows XP maybe the
Vostro 1500 Evalue system N0415018 offers better value?