There are several computers out there that will do what you want.
You have to keep in mind a new computer will more than likely come with Windows Vista and it seems like the venders are taking their own sweet time about getting software and drivers Vista compatable.
I do photo and video editing, but mostly as a hobby.
My machine has a AMD 64X4200 duel core processor with 2 gig of ram and a 250GIG hard drive and works great.
I use Adobe photoshop CS2 for now and it doesn't seem to slow down at all.
My monitor is a Viewsonic 22 in wide screen which does the job just fine.
As I said before, check and see if the programs you have will work with Vista.
Good Luck.