Help with sync between Dell Streak 7 and my PC files

Hi,

Can you explain why I am not able to tranfer any (nada, zilch, the big 0) pictures, video or sound files from my pc to my brand new Dell Streak 7?

I purchased a Dell Streak 7 from Amazon, downloaded the drivers for my pc and installed them.  Downloaded Dell Mobile Sync Software and Installed. I open the software on my pc, I connect the 30 pin adaptor, the Dell Streak says I'm connected. I activate internal USB storage as requested.  All my picture, movie and sound files appear on the large right area in the Sync Software. The Dell Streak 7 icon appears in the left column of the software.  I try to click and drag the picture from the left field over the right Dell Streak Icon.  It has the say "No" symbol. 

What don't I understand about this? 

Thanks so much.

David