Install with root filesystem on Compact Flash

[John Wendel]

I'm building a new box and I'd like to install the root filesystem on 
a compact flash card. Not too hard. But I want / to be read-only, to 
avoid premature wear out of the flash.

It seems that I need to use a "union filesystem" that will let me 
mount some writable directories (/etc, /var, ???) from another device.

My brain is too tiny for this stuff, so I need some help. URLS, 
whatever, would be appreciated. If you've successfully done something 
like this, please share.

Thanks,

John