I am trying to add customer comments to the onepage checkout review tab. I would like to eventually post the results in the sales order email that is sent back on checkout. Based on research I think that I need to build an observer to tie to the event checkout_type_onepage_save_order. Any help with this is much appreciated.
The frontend events that you'd be looking at would be:
checkout_type_multishipping_create_orders_singledepending on if you allow this
There is an extension by Magemaven which does exactly what you're looking for, see it on MagentoConnect.
This tool will allow you to download the source code directly prior to installation.
Let me know if you need any further explanation.