Sub domains mod rewrite help wanted

[purple]

Hi

I have a few sub domains. SE have picked up the parent domain ie instead of

red.widgets.co.uk
it has picked up widgets.co.uk/red

Although SE have picked up both ways in some cases, could this lead to duplicate content penalties?

Would a mod rewrite solve this?
being a totally novice on mod rewrite could someone suggest some code.

I sure I asked this before!!