Dell computers don't come with wireless adapters standard, but you can customize your dell to include a wireless adapter for a price - or you could just buy one separately. There are usb wireless adapters, and internal cards. The usb ones work great, and you can move it from computer to computer easily.
Or a Microcenter one for about $20 (this is wireless N): Microcenter USB wireless N adapter. A buddy of mine just picked up a wireless N USB adapter for $14.99 at microcenter last week, and it worked great.
Asking about the best PC under $700, are you looking at the best Dell under $700, or is building your own an option?
In terms of "internet, photo, & sound" do you mean you will be doing photo editing, like photoshop? What do you mean by sound? Just listening to music, or actually recording?
Not sure what your title for this thread is, you might want to edit it, so that you might get some more views/replies.