Hello jimg77,
Welcome to the Q&A Forum!
Made a quick movie with my Canon PowerShot SD450, and had the camera turned sideways to better fit the subject
Of course, I've never done that!

Seriously, if you have a recent version of Canon ZoomBrowser, you can rotate the video file to the correct orientation.
In the Tasks sidebar, click on Edit > Edit Movie > Right-click the selected video and select Rotate.
You can download the latest update of ZoomBrowser. Make sure to select the one that is compatible with your operating system:
http://www.usa.canon.com/consumer/controller?act=ModelInfoAct&tabact=SupportDetailTabAct&fcategoryid=224&modelid=11939#DownloadDetailActVideo editing programs usually have this feature, as does Apple QuickTime Pro.