1) In ArcGIS 9.3, you can use only points as barriers. If you need to create many barrier points and use these barriers in many projects, I would suggest you to export all the barriers to the feature class. You will be able to use this layer when using the Load Locations tool in order to load barriers to the Barries sublayer in the Route layer.
2) If you need to export the Route layer geometry to a GPS, you should check your GPS device model specification in order to figure out what data types are supported there, and thereafter export your Route layer to a shapefile, for instance, and then use ArcGIS tools or 3rd party tools for converting the shapefile into a custom format. Regarding tablet PC: what application are you planning to use on the tablet PC? The logic described for the GPS device can be used here as well, though.