HP and Compaq are one in the same now, IIRC. Another brand to look at is Avartec (sp?). I got one off Wal-Mart's clearance rack for $530 and it has served me well. Best pre-built computer I have bought, including desktops.
Big screen is a matter of prefrence. I have a small screen, which I vastly prefer to my friends big screen just because of the smaller size. Smaller screen can help with the weight.
No less than 512MB RAM if he can afford it, and is doing photo stuff.
I'd reccomend an ATI or nVidia graphics chip over an SiS or intel. Might not be so critical with what he is doing, but there just seems to be a lot more support for ATI and nVidia than anything else.
+1 to charby on processor, although if you go with the 800 MHZ FSB P4, you could probably drop down to the 2.4 if anyone offers it anymore, and if you would save a bit of money by doing so. I wouldn't go that low with 400 or 533 though.
As for wireless, in my experience my external card works better than the internal one. Seems to pick up a signal better, but the downside is that you take up a PCMCIA slot with it, it sticks out, and it is something to lose.