I think if I was spending $700 then I would certainly consider a low end new since it precisely meets your specs. That way you also get a years warranty or for a bit more an extended coverage.
It seems like 90% of the folks that sell used only remember what they paid for it and struggle with selling at a fraction of that price.
And the other 10% good deals get eaten up quick.
Take a look at this link to ebay for a notebook like I have, its an HP, nothing specatacular and works with most games with a dedicated moblilty ATI 9000 special modified card to mimic the 9200. The specs are slightly better than what you request but so are the prices, though some can be had in the $600-$700 range. The search is for completed so you can see the prices. I like to use ebay as a benchmark tool to help determine notebook prices.Ebay completed search for X1000/ZT3000/NX7000
The dell equivalent 8500/8600 is a nice performer at a modest price. Both have the nice big 15.4" screen and dedicated video card you want (the Dell has far more choices though and can be interchanged much more easily). the HP is a bit more solidly constructed and the plastic in the chassis does not creak and groan when picked up with one hand but the dell has for more users, with easier/cheaper parts, easier to fix. and also it is possible to upgrade in a limited sense, due to the wide range of options they are offered with and the large user base meaning lots more parts to find at a cheaper price.
So if you wish to stick with very modest performance buy new, and I must say that R3000 though modest does give alot of bang for buck in a new machine and I have read good reviews by purchasers very satisfied and happy with the money they saved with a machine that met all there needs. I have not looked at Dell systems lately but they have always had an equivalent matching system and with deals/coupons can usually be purchsed for a bit less than the HP product, just that groaning from the plastic in there low to midlevel notebooks has been a real turn off for me though in reality it does not mean anything as it performs as good or better at a slightly lower price if your willing to hunt the internet for deals/coupons
If you would like to have slightly better performance look for used, something from HP/compaq or Dell as they both always had good modestly priced mid performer machines at half the price of the big guys (Sager/Sony/etc) but of course without the latest and greatest.