How to format USB key so it works in windows ??

[spinnerlys]

....which is what "doesn't see it all all" typically means. All we can go on is what the OP stated, and based on that, Windows doesn't recognize the device at all, which would indicate it also can't format it. If the facts are otherwise, the OP didn't specify.

As he didn't state that the OP looked at the place I specified (Disk Management), I thought it would be appropriate to mention this method.

It's not that Windows Disk Management can be as easily reached as Disk Utility under Mac OS X.

And since aduteau isn't coming to the thread anymore, maybe s/he has solved the problem.