[CentOS] Linux driver for HP Laserjet 3500 printer - yum won't install

I'm trying to install the linux driver for an HP Colour Laserjet 3500 in CentOS 5. I've installed the kde.repo (with appropriate priorities set up), but when I try yum install pxljr-1.1-1.i386.rpm, yum says 'nothing to do' - is this because the priority protection won't let it install from the kde repo? The alternative approach seems to be to use yum localinstall with the downloaded package, but then I get the message that 'the package is not signed'. So how do I resolve that please - the instructions regarding 'signing of packages' don't seem very clear to those of us who weren't 'born and bred' on linux!

Thanks, Andy