Changing "image size" to get *more* pixels (blowing up)

Hello. I would like to resample pixel images *upwardly* - say, changing them from 1600x1200 to 3200x2400 pixels. I do know i cannot gain any information and i could print the original pictures, just with very few pixels per inch. But then the image is too blurred. I use Paint Shop Pro 8 and Photoshop 7.
I think i heard, when scaling up, one should use a noise filter? How about unsharp mask? Do you have any other tipps, experiences, or just useful links? Thanks a lot!

Henrik,

It is ALWAYS worth applying a fairly hefty dose of Unsharp mask after re-sampling

thanks!

Sure, thank you.