Just me, because I watched Windows chew up more and more memory for so many years, I always lean towards having a little more than the bare minimum of memory. I know Win 7 & 8 aren't as bad as Vista was, but I'd see if I could find a machine with 6GB of RAM if I were you. Also, IF you plan to store a lot of video on your HDD, you might go through 500GB faster than you'd think.
I'm looking for a laptop for my mom and Office Depot has some pretty good looking (specs, price, etc.) machines (15.4 touchscreens) from Lenovo and Toshiba in the $470 to $570 range.