replacement of front wheel bearing

Is it possible to replace only the wheel bearing (front wheel) or do I have to replace whole wheel hub assembly? Some cars have enclosed units so you cannot access the inner bearing.

I have a 1997 vision and had to replace the entire hub assembly. You (or maybe just me) can not just buy a bearing :banghead: . It all comes as one unit. It is not hard to change and I think changing the hole unit is actually easier then just the bearing. Good luck!