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Installation instruction for Rosetta are found here:
Rosetta is an optional install that allows Intel microprocessor Macs (Macs built in 2006 and newer) to run programs originally created for PowerPC microprocessor Macs (basically Macs 1998-2005).
OS X 10.6 'Snow Leopard' is the last version of OS X that will support Rosetta.
Check to see if the driver downloads HP offers are newer than the ones on the install disc. The downloads are from early 2008, and specifically say they're for OS X 10.5 only.
http://h20000.www2.hp.com/bizsupport/TechSupport/SoftwareDescription.jsp?lang=en &cc=us&prodTypeId=18972&prodSeriesId=1161389&swItem=ma-58935-1&prodNameId=114078 0&swEnvOID=219&swLang=8&taskId=135&mode=4&idx=3
If they don't work, it's probably time to invest in a newer all-in-one printer.
It seems like you're suggesting that the original drivers for the LJ 3055 were actually written for the pre-Intel Macs and that's why I was prompted to install Rosetta when I recently tried to use the original software installation CD (from HP) with Snow Leopard.
Not exactly. The Full Software Solutions package is a "Universal Binary," meaning that the software it installs should support both Power PC (pre-Intel) & Intel Macs. The description says, "It supports OS X 10.3, OS X 10.4 (Power PC and Intel Core)." There is also a "Release for Mac OS X 10.5" on the downloads page & its description says, "It supports OS 10.5x only (Power PC and Intel Core)." It looks like HP intended for 10.5 users to install first the Full Software Solutions package & then the "Release for Mac OS X 10.5" to update the software for 10.5 compatibility.
So the main issue is if any of this will support Snow Leopard (10.6). If HP support can't tell you that, the only way to find out is to install it & see. If, when you try to open the installer, it tells you that you need to install Rosetta, do that. (It can't hurt to have Rosetta installed.)
It may be asking for Rosetta because the installer itself and/or some of the software other than the drivers in the full package are not universal & so must run under Rosetta emulation. (An installer is a program that installs various software. Don't confuse it with the software it installs.)
Regarding Apple creating its own drivers for third party products, it doesn't do that. It often works with OEM's to adapt, update, & distribute their drivers with OS X, but the actual code is supplied by the OEM. Unfortunately, it is all too common that an OEM won't update the software for an older model, so I'm afraid that is a dead end for you.