There is an ia64 kernel bug introduced in 2.6.7, which may lead to hang on boot. See http://marc.theaimsgroup.com/?l=linux-ia64&m=108822933326048&w=2 for details and possible patches.
2.6.7-1.441 is OK. 2.6.7-1.448 and and 2.6.7-1.457 both hang on my ia64 machine.
Kernel 2.6.7-1.469 booted fine on ia64.
2.6.8-1.603 is OK.