Apps are tied to your Gmail account. Simply sign into the same account on the Fascinate and you will be able to download everything you have purchased in the past. However, some free apps may not show up in your download list. App settings will not transfer over, unless the app has a built in function to export it's settings to your SD card and reimport them into the fresh install. LauncherPro is an example of this. Another option, if you are rooted, is to use a backup program, such as Titanium backup, to backup apps + settings on the Nexus and restore them on the Fascinate. Some people report success with Titanium. However, I personally have never gotten a restore to work. As far as system settings like ringtones and wireless networks, it only takes a few minutes to reconfigure those manually.
Edit: Looks like Kevin was posting at the same time I was. I agree AppBrain is even easier, if you take the time to figure out how it works. I love AppBrain.