1. You can just copy the entire iPhoto Library folder over to another drive. Then start up iPhoto holding down the option key, direct it to the "new" library, and then delete the old library. The new one will become the default library (it is important to be sure the drive is mounted when calling up iPhoto after that, otherwise it will create a new blank library on your boot drive when it can't find the "default" one). This works the same in iTunes for music, BTW.
2. What dmunroe means is that once he reaches 10,000 photos in a given library, he creates a new one. iPhoto supports multiple libraries but can only load one at a time.