I tried K3B, but never had any luck in working it out.
One of the guy's at my LUG told me to try this
scans the "SCSI" bus to detect your CD writer and gives you the number (eg 0,1,0) that you use in the next command. My writer is SCSI, which actually simplifies things for me. If yours is IDE you will either have to use the SCSI/IDE emulation, which you may need to find out about or, I believe, it can all be done with IDE these days - I'm not sure.
#cdrecord -v dev=0,1,0 cdname.iso
burns the CD from the ISO image you created in cdname.iso -v says verbose so that you can see progress
It worked for me, and it's done from CLI so it means that you can just su
into your root account.
Obviously you need to make sure that you have the various cd burning tools available
Oh, and I'd say that if you're gonna give gentoo a go, print off the install guide and the desktop set up guide. And then to get your self up and running the quickest, do a stage 3 +GRP install. If you do the install (even stage 3 takes a while), and then you just "emerge" the kde (for example) the emerge takes a looooooooooooong time (kde took 15 hours for me). Emerge will download and then compile each of the individual packages one at a time, hence I suggest you try the stage3 + GRP
p.s. When I tried to do the burn with K3B when it got to the bit about changing/modifying my fstab, it killed the scsi emulation that I needed for my burner. I understand it's very good, but can be a little confusing to set up the first time.