if you up the dpi in photoshop, you're just adding more information into the same space, it doesnt make the image quality any better. Shoot with the highest quality setting on your camera and that's as good as you're gonna get. My Nikon D80 shoots at 300dpi, so if you're looking at printing off quite a few images professionally in the future, prolly good idea to get a relevant digital camera. Otherwise, cheat by making a 300dpi blank doc in photoshop and cutting and pasting your photo onto it, stretching if need be... the image might appear to get a little blurrier, but the same thing will happen if you up the dpi of a standard image anyway.
I've always found that digital camera pics come out at 72dpi but at a ridiculous physical size. So I usually up the dpi to 300 and reduce the physical size. You have to juggle the numbers a bit but I usually end up with a good quality image at a reasonable size.
This is a bit obvious, but I hope it might help someone!