kernel 2.6 difference between g4 and powerpc kernel

[Peter Spuhler <pspuhler@spuhler.net>]

I have a dual CPU grey-green tower Mac which i was under the impression was a 
G4. I'm having issues running the G4 flavor of kernel 2.6
cat /proc/cpuinfo returns
processor       : 0
cpu             : 7400, altivec supported
temperature     : 31-33 C (uncalibrated)
clock           : 450MHz
revision        : 2.9 (pvr 000c 0209)
bogomips        : 894.97

processor       : 1
cpu             : 7400, altivec supported
temperature     : 39-41 C (uncalibrated)
clock           : 450MHz
revision        : 2.9 (pvr 000c 0209)
bogomips        : 894.97

total bogomips  : 1789.95
machine         : PowerMac3,3
motherboard     : PowerMac3,3 MacRISC Power Macintosh
detected as     : 65 (PowerMac G4 AGP Graphics)
pmac flags      : 00000004
L2 cache        : 1024K unified
memory          : 256MB
pmac-generation : NewWorld

Anyways i tried running kernel-image-g4-smp  and it froze right after loading 
the initrd. I then tried kernel-image-powerpc-smp which works great. I'm 
wondering what is the difference between the two kernel-images and why does 
the G4 image not work for me? Also what are the advantages gained by running 
a g3 or g4 kernel as opposed to vanilla powerpc?