UPDATE:
I now have Puppy 4 running pretty flawlessly on a Thinkpad 600X, PIII (500 mHz) with about 300 mb of RAM. Installed icewm, set it as my default by killing x and running xwin icewm, and edited /boot/initx (I think that's the file name... I'm on a different system right now) to disable rox, as it's a memory whore. I'm still looking for a .pet for a better file manager, but without rox starting as default and loading its ugly icons, I have a clean desktop that's running faster than my HP (2.7 GHz Celeron-D, 768 MB). I also have Sidux installed, so I just added Puppy to my grub bootmenu for Sidux, as Puppy's version of GRUB sucks and half the time it just loads the grub shell, forcing me to boot manually (boot /dev/hda1/vmlinuz-x.x.x.x). rt2750 and rt73 both load at startup, and the legacy drivers don't have the connection speed problem inherited with the new drivers packaged with Debian derivatives (In Ubuntu, I have to manually set the MAC address and force a connection speed above 1mb/sec EVERY TIME I connect, and the scanning and dhcp settings always get fucked up). I even replaced my CMOS battery (anyone with an old thinkpad probably noticed that the factory battery sucks, dies quickly, and forces 2-3 reboots to actually load the system) with a 3v watch battery and just taped it all together. I was thinking of setting a boot password, but from what I've heard, if my CMOS battery dies again, I'll pretty much be fucked, as the bios won't recognize any of my set passwords (boot, hdd, or bios) after a new battery. I tried fluxbox 0.9.9, but the right-click settings are messed up, and the menu doesn't stay open (I think it was a conflict with rox, as I didn't try running fluxbox without rox opening), and it wasn't properly supporting the /.fluxbox/xsession bootup script. Openbox is okay, but running an [include] on the obmenu file wasn't supporting the Puppy menu.
Dogs may not be able to read, but they can definitely breathe life into old systems. Where DSL failed for a full hdd install, and Ubuntu minimal install failed (see: lack of driver support to install xorg, wm, and basic applications), I think I've done alright.