Trying to get Unbuntu 6.1 server AMD64 installed and it sticks on the part:

.
Decompressing the kernel
Booting the kernel

Seems to be quite a few others having the same issue, I am having this on a Dell Poweredge SC1435.

Anyway quite a simple fix, there are various different syntaxes for turning off APCI but I will detail what worked for me anyway.

Upon booting off the CD press F6 on the install from CD option, there you can enter boot parameters.

Currently mine ended with ..quiet --

Delete the quiet option so you get lots more information on the screen and add the following after -- :

noacpi acpi=off pci=noacpi

Then hopefully you should be able to get Ubuntu installed ;)