Given a daily production of files named:

productNew_2011May20.txt
productMod_2011May20.txt
productExp_2011May20.txt
(where the product* string remains constant, but date changes)

Can anyone suggest a 'batchable' way in DOS to rename the files to:
1_2011May20.txt
2_2011May20.txt
3_2011May20.txt

I am having a hard time retaining the last 9 characters in my copy/rename command.

Or, alternatively, is there a way to invoke the YYYYMONDD as a part of my filename from scratch? Thanks.