T23s can't use ACPI, in fact they'll refuse to install unless you explicitly disable ACPI on the command line.
I'm guessing your old kernel used apm and the new one has ACPI (statically compiled?) and hangs when it doesn't work.
You'll have to interrupt your boot manager (grub or lilo), select the new kernel and then add
to the end of it. It should then boot fine.
Then edit grub or lilo to tack that onto the end by default and ensure apm is enabled. The relevant info is here, so I won't repeat it (applies to Debian as well): http://www.ubuntuforums.org/showthre...t=thinkpad+apm
And yes, I do have a T23, and it is pretty damn annoying when you first see this happen.