The two Photoshop tools I always turn to are
Smart Sharpen (CS2 only) and
Unsharp Mask (all versions). There's also the option of manual sharpening with the
Sharpen tool. If it's a more complicated job, there's a technique for sharpening with a mask which is a bit in-depth to go into here. On top of that, I have a couple of third-party plugins for sharpening (although I don't usually need to resort to them).
I've downloaded a copy of your image and I'll give it a go anyway. I'll let you know if I have any luck.
EDIT: (Some time later...)
I've had a go, although I'm not really happy with the results. I tried just using Smart Sharpen and USM, but there was too much noise in the photo that got sharpened too. I ended up using a Hard Light blending mode/High Pass filter technique and then added a layer mask to lessen the effect on the areas where the noise was obtrusive. This is the JPG:
http://www.waterden.net/stuff/HighPassSharpened.jpg
(be warned - it's a biggy. Nearly 3mb, because I didn't want to introduce any more artefacts than I had to). I also have a ZIP file of the PSD I created if you want it (although that's even bigger - nearly 22mb).