How to open wb in same session under Vista

Before I re-installed Vista (had to) and Office 2007, when I had an Excel 2007 workbook open and then double clicked another Excel workbook via Explorer window, the second workbook would open in the same Excel session; i.e., not launch another instance of Excel. Is there some setting that I can set in order to be able to use the same Excel instance whenever I open multiple workbooks?

Thanks

Thanks, but I'm not sure you understand my problem. I already have Excel running and a workbook open. When I browse to another Excel workbook with Windows Explorer, and double click to open that workbook, or right click to 'Open' it, a second instance of Excel always starts before loading that second workbook. That means I have each workbook running in its own instance of Excel. This not only makes it cumbersome to toggle between the two workbooks, but more importantly, I cannot copy from one workbook and paste into the second workbook. This was not a problem before I reloaded Vista and Office 2007.

Thanks for your help.

Thanks. I know that works but it was a pain. I think I found the solution. I created a new Windows profile and logged into it, I do not have the problem; i.e., I can open multiple workbooks in a single instance of Excel simply by double clicking the file in Explorer. Thanks.