Hi Ben
If your 'Approval Comments' are from SharePoint then you need to add a new Data Connection, select Receive Data and then select 'SharePoint Library or List'. Type in your SharePoint Form Library (That is content approval = yes) then select the form library, click next. A list of fields is then shown including "Approval_Status" and "Approver_Comments". Select the ones you want and click 'Next' and then Name the connection and click 'Finish'. Now you can display the approver comments from SharePoint in Infopath.
Or,
Your 'Approval Comments' are in Infopath and you need to get them into SharePoint. In your form go into tools and Form Options, select 'Form Library Columns' and add in the field that you use for the Comments. Publish and then job done.
I hope this helps
Adam