Need to enlarge and sharpen an image - Which tool to use?

Gimp
Photoshop

It doesn't sound like an issue of which tool to use, but rather how to use what you've got. A quick Google search turned up the following…

http//www.gimp.org/tutorials/Smart_Sharpening/
http//world.std.com/~mmcirvin/gimp_tutorial/sharpen.html

I can tell you from having worked with various types of crime scene footage that there is a slippery slope between enhancing and modifying an image. As with everything else we do, document, document, document.

There is an Adobe Photoshop book dedicated to the subject.

Something you should peek into
http//www.gimp.org/tutorials/
http//registry.gimp.org/

First are some tutorials on the usage on GIMP, some of which may be of use for what you plan to do, second is the "registry" for all aoptional plugins for GIMP, where there may well be something useful.

jaclaz

You might also want to have a look through this blog - http//forensicphotoshop.blogspot.com/ - its obviously centered around photoshop, but I would imagine the techniques could be transferred to GiMP…I say this not being an expert of course!