right now my site has got 120 backlinks and is a pr4 site...im plannign to change my joomla sef component that means all my links will look different now. Does this mean that all my hard work is lot?
Google will not automatically figure out all the changed links. You have to work out a scheme to redirect all the old links to new links. If not too many links, do a 301 permanent redirect will transfer all your PR values to the new links.