Hi

Looking at your requirements I would recommend getting something like this:
Asus F5VL-AP128C Core 2 Duo T5450 1.66GHz 2048MB 250GB 15.4" TFT DVD±RW ATI X2300 w/128MB VRAM Windows Vista Home Premium - Ebuyer

That would run your sims 2 game fine, it has vista but as long as you run the auto update on sims 2 once it has been installed it should run fine.
Will you be wanting to do word processing and spreadsheets etc; if so I would recommend buy office with the laptop as it will work out cheaper.
If this is just for home use I would recommend getting Office 2007 Home & Student Edition. This comes with, word, excel, powerpoint and onenote.

The home and student edition if about £80, so you would be looking at spending just under your budget for a decent laptop.

One thing that I always think is worth sorting out when you buy a new laptop is anti-virus/internet security. Although you can get AVG for free there are a number of ones out their that are paid for but that bit better. One that I highly recommend is ESET NOD32. If you think that is something that you might be interested in just let me know and I will get you a price.

Out of interest where abouts are you located as I may know of some decent shops in your area?

I hope this helps, if you have any questions just let me know.
Many Thanks

Leo