also depending on what you want to use a higher rez pic for, you can (if this suits your purpose):

use photoshop to resize the image, add a layer below the layer with the pic... fill it with white. then on the layer with the pic, adjust the opacity to like 50% or even lower... you can then type text on a layer on top of the layer with the pic... the enlarged pic won't look too bad if used in this fashion

if you need a higher rez pic and enlarged it with PS, and just paste it into an article on a website for example, that pic will look pixelated, as i'm sure you know of enlarging a pic from a lower rez pic.

good luck