Bilou_gateux,
In the /var/log/binlserver.log you can see what happens.
1. The client tells the UDA the vendor and type of the network card it uses, by contacting the binlserver on the UDA.
2. The binlserver checks its database to see if it has drivers for that network card and if so replies with the inf and sys filenames of that driver.
3. The client then uses tftp to download those drivers.
You can see in the log what the vendor and type the client requests from the UDA. (Usually something like PCI\VEN_8086&DEV_1229 ) This string should match exactly with the strings in the inf file you have supplied. Also the inf file should list the exact name of the .sys file (without path) that should be loaded for the specific network card.
Hope this helps, and by the way, check if the client is not requesting a lowercase filename while the actual file is uppercase or the other way around.
Good luck