I have been running an HP Laserjet 8100 on my Linux box for a while and everything has been fine, i'm able to see and print from all trays.

I recently purchased a C4780A dual 500 sheet feeder but i am unable to see the 2 trays where i should see them as tray 4 and tray 5.

Can anybody help?

Sorry, I can't help, but do you remember what driver you were using for the HP LaserJet 8100. I normally just use the LaserJet4 driver for anything HP and it works fine. Not in this case though.

You can edit the .ppd file for the printer and add in those extra trays..

a .ppd file is a Postscript Printer Definition file. It tells the print system all the information about your printer and it's features. where the margins are, the non-printable areas, the resolution, paper trays, duplexing etc..

I can't tell you specifically what you need to change but if you look through the file you may just find a few lines you need to uncomment to add support for those paper trays.

You can find more information on .ppd files on adobes website.. the wikipedia even has some links
http://en.wikipedia.org/wiki/PostScr...er_Description