RAW is proprietary to a given manufacturer, and even when you have the same file extension (like Nikon's .nef format), there are differences between files generated by different camera models using it.
In order to have a viewable/editable image, you need to convert this file into another format first. Some viewers can do this "on the fly" so that you have a viewable image. But, they're still doing the conversion (even if used just for displaying the image).
There can also be a big difference in algorithms used between different raw converters. So, the output may be quite different from one versus another, especially for things like white balance, tone curve used and more.
If you plan on editing the file after the raw conversion piece, your best bet is to stay with a 16 bit format to reduce any potential posterization due to rounding errors. Then, convert to JPEG as a last step. But, there is no set way to go about it. Each user tends to have a preferred workflow for images.
There are a number of free products available that can convert your raw files to another format for you, so that you can edit your files further using something like Photoshop (and most give you the option of saving the file in a number of ways for further editing). Adobe also has a plugin called Camera Raw. But, you'd need CS2 to get support for the plugin that works with your D80. Nikon also provides a plugin in the software that comes with camera. But, it really doesn't let you do much. They'd like to sell you Nikon Capture (a $99 option). You'll probably find a trial of it with your camera.
One popular free product you can use to convert your raw files is UFRaw (and there are a number of others).