I looked for my post and I was -partially- right. It was one of the more experienced people (so to speak) that replied to my, virtually identical thread: stief and then sberlin (one of the software developers).

stief tried to give me an explanation thru his own knowledge (thanks man) , but then a software developer came to clear thing up.
Here's what he wrote:
"Red rows in the library mean that the file is not shared. For incomplete files, sharing means that the file is eligable for partial file sharing (PFS). A file being shared via PFS will not be found by normal querying methods, but is instead shared only through the "download mesh". When you download a file, you insert yourself into the download mesh. As other clients download a file, they try sources that are advertised in the mesh.

The download.dat (download.bak being an automated backup of download.dat, used when LimeWire senses that .dat is corrupt), as stief mentioned, is an index into your incomplete files. It keeps track of exactly what byte-ranges have been downloaded for any given incomplete file. If an incomplete file is not listed in download.dat, then it will not be shared through PFS (and will be listed in red in the library)."

Neat huh?
You understand of course the 'so to speak' at the beginning: a software developer is, well, indeed a whole lot more experienced than most regarding one of the apps he helps create and improve.

__________________
iMac G4 OSX 10.3.9
RAM 256MB
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps

"Raise your can of Beer on high
And seal your fate forever
Our best years have passed us by
The Golden Age Of Leather"
-Blue Öyster Cult-