There are two addresses to upload...have you tried this one? http://www.wincustomize.com/upload.aspx
I've had pretty good luck uploading via FireFox without Flash installed at this link. http://www.wincustomize.com/upload2.aspx
The first one does not have a counter, so use your browsers progress bar to guage if it's uploading.
The second one has a counter and I've found that if it does not start counting up, closing out FireFox and then reopening it and trying a second or third time works for me.
I tried these alternate uploads that CarGuy just gave you, but I got them from AzDude and they worked for me, so give them a shot they definitely work........thats it from me,...the Thugorino
Thanks CarGuy1. I'll give them a try.