I can tell you that your budget will allow you to get a good laptop. For what you are going to use it, I would suggest HP or Toshiba. You can get a decent one with 3 gigs and 250 BG's of hard drive space. (you said memory but it's technically called storage capacity. Memory is the same as RAM)
The picture editing will likely use a lot of ram. make sure you run at least 2 gigs so it runs smooth. I have used Photoshop on my laptop that had 1 gig and i got just a bit of lag. You can also increase your paging file inside windows (i'm assuming that's your Operating system). Make sure that you are buying DDR2 ram and not DDR1. There are very few DDR1 new laptops out there but they still exist. Also remember that the new laptops are coming out with Windows Vista and this Operating system uses a lot of system resources which is why high end laptops still run slowly. I would run WIndows XP instead. Or better yet just buy a MAC.
As for your processor. Definitely go with Intell. Buy the DUO core not "DUAL" core. As long as your over 2ghz speed you should be okay. You can go with AMD Athlon too but they run a fraction less in speed but they are a bit cheaper.
Don't worry too much about hard drive space. The 250 that you are seeking is perfectly fine. I would recomend that you partition your drive so that you have a partition for your operatng system and a partition for storage. This helps avoid loosing your info if your system crashes. It is easier to recover this way. Go to a computer store and make sure you buy insurance for 2 or 3 years. Don't buy insurance for longer than that because in 3 years, your laptop will be a turtle compared with the new models.