What happens when you try to download one & it does not work? Does an error come up? You can try to turn off the phone & remove the battery for a little bit
What errors are you getting when you try to install the application? Here are the steps to make sure you're going through every thing properly. Hope it helps!
Just to let everyone else know..
I came across this same problem. I proceeded to do a battery pull and this worked. It could have been that as a fix, or it could have been a market issue resolved over time.
Does anyone know what Error 18 means when an app you try to download does not install.???