How are you scanning the negs. My film scanner software has a function to convert from colour neg to colour positive. As you've probably found out a straight colour reversal doesn't work. This is because neg film has an orange mask this has to be removed in the conversion process. My scanner software has settings for various film types as the charateristics are different from film to film.
You could try VueScan if your scanner is supported. It can be downloaded here
VueScan Scanner Software and it's free to try it. If it does the job then you'll need to pay $40 to get a fully functional version.
I've also found this article which explains how to do the job using just photoshop and the curves tool
MacEdition : Features: : June 26, 2003