To create a template in Report Studio, simply create a report with the formatting you want (ie, lists, graphics, headers, footers etc). Save the report.
Then when you create a new report in Report Studio, the window comes up to choose the type of report (Blank, List, Crosstab etc). You will notice there is a folder called 'Existing...'. Choose existing, and navigate to the template report that you saved. This will create a new report using the report that you saved as a template.
As for how to apply the template to existing reports, im sure it could be done, but I dont know an easy way to do it.
J