The New Debian-Installer works wonderful for most PPC. The only ones that are really having trouble at all, are the really new hardware (less than 3 months old in release) and Old-World machines.
Even then workarounds exist... and most things just work.
As far as Scanners there are a coupla things to look at: [link|http://www.sane-project.org/|SANE Project Home] and specifically [link|http://www.sane-project.org/sane-supported-devices.html|Supported Devices] there are two branches Stable and CVS. Stable is barely used by any distro these days, CVS is where it is at.
But, if your scanner is in Stable, but not "complete" it may be in CVS. In any case you should check out both versions.
I believe Debian has 1.0.13... yep.
They even say:
Use the CVS lists instead if you need the links.
So, your choice. I went with an older Epson USB 1660, it supposedly works just like the 1650. Haven't gotten it yet from the place I bought it from. It has a tracking number from UPS, being Economy-Ground... well when it arrives, it'll show up.
P.S.: I have been following Debian-Boot for quite a while. It is amazing the difference in 1 year the progress D-I has made. Shoot the PA-RISC installer even is going to the 2.6.x kernels as default and removing the 2.4.x kernel from choices. Significantly, it appears other architectures may even follow this, but still leave 2.4 for only some arches. Two arches having a big problem is MIPS-EL and M68K, the wanna-build queues are not serviced by enough processors... they are BARELY keeping up (actually not), but there seems to be resistance to allowing more machines to access the wanna-build queues. (something about archive masters being pissy or something)