http://www.google.com/search?q=scrollbar+%27left+side%27 doesn't give any indication that this is possible in Windows (although there are hints that it can be done on a web-page and in Linux).

It doesn't seem an unreasonable request, so better contact Microsoft, so that they can implement it in the next release of Office and/or Windows (called Longhorn). I'm afraid you'll have to wait a few years for it. It must be something their usability labs missed.

Kees