How do I access the backup of my iPod Touch?
If you are using Windows 7, the backup file is located here:
C:\Users\[yourusername]\AppData\Roaming\Apple Computer\MobileSync\Backup

If you are on Windows XP, I'm sorry, and your backup file is located here:
C:\Documents and Settings\[yourusername]\Application Data\Apple Computer\MobileSync\Backup

The backup file is a database file. You won't be able to browse it manually. You can either restore it to another iOS device, or you can use specialized software to extract the data for you. This is but one example of software that does this: http://www.iphonebackupextractor.com