Hi all, happy new year 2008!
About Duplicate Files, i have always the same problem, files have the same size so same contains, but have differents names, so i don't find the good way to have a good results, we have the filename, filename&size,md5 checksum, but not just the size parameters and it's missing...maybe a request or i forgot something ? 
That's what the MD5 checksum option is for. It will only compare two files if they have the same size.
If two files have different sizes then they are obviously different and not worth comparing.
If two files have the same size (and different names) then it's still quite likely that they are different (especially with formats like BMP where two completely different images of the same resolution will be the same size), so Opus calculates MD5 checksums of both files in order to see if they are the same or not.
Thanks Nudel, but for me in this case, i have a hard of 250 gigs full of Divx, and i try to use the MD5 checksum and it takes to much time just for the first folder, and it seems that dopus bugs because when i would to stop the operation i had a "no response" so i was obligated to kill the dopus process...i will retry and i give you the time that it tooks just to have an idea for a big process, i'm already scared 
Yes, it can take a VERY long time... but like nudel said, a simle 'size only' comparison can be pretty worthless. Let's even take an example from the sort of files you've mentioned... DivX movies. I've got tons of DivX movies that I've converted in order to be a certain specific size. They are all different movies and EXACTLY the same size, so such a mundane comparison would be useless.
I'm not sure what you think you'd gain by comparing JUST size... but if that's all you want to know, why don't you just go to the root of the drive, switch to flatview mixednofolders, and sort by size and then see if you can narrow the scope of your "real" comparisons after perhaps reorganizing your data a bit.