Unable to open copied files from computer to device (mount as disk drive) - HTC Desire S

I connected my phone as a disk drive and put some files ( .png ,.jpg ,.swf ) in the sdcard. I am unable to open those files on the phone. I am unable to find those files in the gallery of the device, either. When I checked details from Astro file manager it is showing the extension .cp$ on all the file, as in filename.png.cp$ I am not getting what is the problem??