sharpening images

is there any way of sharpening images that are small and have been made bigger.

ive tried using the sharpen filter but it looks terrible

Nope. Actually it depends on the original/final sizes, but most likely no.

The reason being is there's not enough image data (detail) to sharpen when you blow it up. A small sharp detail beforehand will become a big blurry blob of color after and the only thing sharpening will do is increase the contrast between these large blobs.

You might try adding noise, basically faking detail and maybe use unsharp mask very lightly, but dont expect great results.