I am sorry you are having problems with transferring pictures from your PC to EVO . First of all what you want to do is to make sure USB debugging is not checked. The way you do this is on your phone, go to home, menu, applications, development and make sure USB debugging is unchecked. After that plug your phone to PC, you should get a notification on your device. There will be 4 choices: charge only, HTC sync, Disc drive and USB tethering. Choose Disc drive and then done. Now it should at this point recognize on your PC. If you dont get a pop up to view files, go to my computer or computer and it should be under removable disc drive. once that is open it will display all the files on your phone that is on your SD card. Look for a folder that says DCIM. That will be the folder where your pictures are stored. Now all you have to do is go to the pictures on your PC and drag and drop the picture from PC to DCIM folder on device.
If this doesnt work we need to know the operating system of your PC - Are you using HTC cable?
Larry ~ OKIESTRO