XP lets you rename files in bulk by simply selecting multiple files within Windows Explorer and pressing the F2 key. When you use this feature, the OS applies the name you enter to the first file and applies the same name with a number in parentheses to the other files you selected (the file extensions remain unchanged).
For example, if you select the following files,
and rename the first file (my.doc) to cat1.doc, XP renames the remaining files as follows:
* cat (1).xls
* cat (2).jpg