A while back I wrote about how to create empty files using FSUTIL a windows build-in command line tool for managing FAT and NTFS file systems. Today I found a nice little free utility called Dummy File Creator created by Nikko Cheng.
You can use the GUI version (dummy.exe) or if you want to include generating dummy files within a script you can use the command-line based version (DummyCMD.exe).
Dummy File Creator can be downloaded from here