If the wire originates in the panel where the neutral bar is grounded to the case (99% of the time this is the main panel unless you're in a mobile home) it doesn't really matter whether it's connected to the ground bar or the neutral bar -- they are still the same thing at that point. It's more "workmanlike" to put it on the ground bar, but that's all.
If it's a small panel and was installed a long time ago, there might only be one terminal bar. Don't go messin' with it unless you know what you're doing.
If it's a small panel and was installed a long time ago, there might only be one terminal bar. Don't go messin' with it unless you know what you're doing.