I've been trying to make sense of the instruction book for PhotoFun Studio 5.0, which appears to be the relevant software.
http://dlc.panasonic-...ng=en-GB&model=DMCTZ8
I hope that the following will help, but I'm not guaranteeing anything!
Open PhotoFun Studio 5.0 (from Start > Programs).
Go to Tools > Settings.
Click Still Picture - Copy to PC
Then under 'Set the operation where there are files with the same name', choose 'Auto' (but see below if that's what's already set) and click 'Apply'
The 'Auto' setting compares the files which are stored in the camera with those which are already on your PC. If it judges that they're identical it shouldn't download any duplicates. However if it thinks that they're different (even though they have the same name) it will download the images from the camera, adding an extra character in brackets onto the end of the file name.
If, for some reason, the program is detecting files as being different (perhaps because you've tweaked them on your PC) even when they're basically the same, you might want to select 'Manual' and 'Skip' (instead of 'Auto') when following the instructions above. That will prevent the software from downloading any files with the same names as ones which are already on your PC, irrespective of their content.
Chris