You can set geotargeting in Google Webmaster tools. Subdirectories with a gTLD is a supported solution and duplicate content shouldn't be an issue; however, we have had canonical problems with English pages across .com, .co.uk and .com.au ccTLDs.
Google claims that they're smart enough to understand that your subdirs are for different countries but I'd strongly recommend changing the content as much as possible. Use different spellings, sentence structure, etc, let the client know that it's also better for visitors to see customised content rather than a general marketing copy.
You can read more about the Webmaster Tools settings here: http://www.google.com/support/webmasters/bin/answer.py?answer=182192#2

