I think computers and GPS'es should be seen and not heard. All of mine are on "mute". nRoute evidently gives voice directions but I have never used it.
Maybe you need to explain what you want to do a little better though. Many people will feel that nRoute is pretty "retro" by today's standards. The only reason I use it is because I like the way it renders my own topo maps on the screen (they look pretty much identical to their appearance on my Oregon, and better than Mapsource can display them).
If you want real turn-by-turn navigation, it is probably not your best choice. Garmin's City Navigator is locked to specific gps'es, although it can be used on different computers. But when running nRoute, my understanding is that your copy of City Navigator must be locked to the gps that you use. Do you already have City Navigator installed on your 76cs? If not, you will have to buy it.
If that's the case, you might look at Garmin Mobile PC instead. You can get a version of it along with a USB GPS for under $100. You can also get a software-only version to use with your own GPS for even less. It is more like a Nuvi with some additional features. I find that it mangles my own topo maps since I break a lot of rules in making them

You could also check out Microsoft Streets and Trips. I grabbed a copy of the 2009 version recently at Staples for about $70 and it included a small uBlox USB GPS which I also use with nRoute.
Then there's also OziExplorer which I like, but it works with raster imagery, so you have to make your own maps and they are not routable.