Thanks for the help Vinod, I got it done before my deadline - I used the FILER dll (available from the MS VFP site) it allowed me to put all matching filenames from all folders into an array.

>>I need to rename the extensions of thousands of files in many sub folders that are all under one main folder - by end of work today !
>ren *.old *.new will rename multiple files
>make a batch file, which will change each and every dir. and then use this command or use a utility like sweep, which issues a particular command in multiple dir.