Okay...what model of curve is it? and how old is it?
By the sound of it its a trackpad you have rather than a scroll ball. These can be replaced either by yourself if you feel competent to do it, or you can give it to a mobile repair place.
As for the crashing, have you tried connecting it to a PC, downloading and installing BlackBerry Desktop Manager and then checking to see if there is a software upgrade available for the phone?
It could even be the case that a full wipe of the phone and a re-install of the operating system would sort the problem but again only if you feel competent in doing that.
