Unfortunately you can’t import custom themes to WordPress.com, even with paid upgrades. Many themes, however, allow limited customisations and you can customise them further with the Custom Design upgrade. Here’s a link to the support doc: http://en.support.wordpress.com/themes/adding-new-themes/
Hi There. Many thanks for your response. I suspected as much. Are there any recommended hosting sites that support wordpress in Australia? We tend to find that US based hosting leaves a little to be desired from a support perspective for Aussie clients. (Unfortunately a function of Australia being a relatively small market).