Hey Xsoliman,
Yes, MHDD passes most of them as OK and many are delaying/timeout.
The weird thing is that sometimes the same sector throws a TIMEOUT, sometimes (a few) AMNF or ABRT, and others passed fine.
FYI, the *very first* time I connected the disc after the platter exchange, and booted with XP restore console, did a DIR and saw under C: files and directories from the 3 partitions! Also, connecting the disk via USB firstly showed me 3 partitions, unformatted.
Then started degrading. Windoze showed me just 1 partition with the full size and now doesn't shows any partitions at all, but the disk appears in the Device Manager.
Running GetDataBack many times got freezed by these reading errors, and ALWAYS (every program) gives me an error reading sectors 0-63.
Ok, I tried to avoid them and when running a partial scan I've seen a lot of
User defined file BMP @sector xxxxxxxxxxxxxx, LBA=xxxxxx, size=0
...
User defined file MP3 @sector xxxxxxxxxxxxxx, LBA=xxxxxx, size=0
and so on.
When I was able to do an image with Runtime's DiskExplorer (brother of GetDataBack) I had the 298 GB as in the above screenshot. Many many many entries related to real files!, but no content... as if the whole image were a giant file assignment table.
I have to say that I've used the strategy "skip block on bad sector found" and took about 30 hrs. Running a "retry each sector" will take 59 days

My goal now is to ignore completely the first 50GB of the disk (which is where the C: partition used to be, for the OS) and try to recover as most as possible the rest of the disk, ignoring the bad parts. If a file is corrupted it's fine. I'm not going to cry.
Also, FYI, the disc is giving a looooot of CRC errors, and I think that's because of the missinformation on the first part of the it, telling wrong values.
Another two screens that could help to realize what's going on.
Thanks to everyone!