|1 - Please do not post in all-caps. All-caps is the Internet equivalent of shouting and is often considered as being impolite.|
2 - Windows, specifically Windows 7, is an operating system. Excel is an application that runs under the OS and is not specifically associated with the OS version. In other words, you can run Excel 2007 under Windows XP as well as Windows 7, just as you can run Excel 2003 under both operating systems.
If your real question is:
Where do I find the Sum sign in Excel 2007?
Then look here: