You have only 170mb free out of 2 gigs of installable application space, and you don't have a lot of applications installed?

Something isn't adding up here.

It is probably something that was downloaded to your rootfs via your web browser. Flash item, etc. maybe?

Also your 5gb free of normal phoen memory have nothing to do with your rootfs or installable application space. It is completely seperate from the two. (unless you've reformatted your phone)

2d