I have two computers that hang at the Tux screen. I have tried booting with several cheat codes including the following:
noscsi noapic
noapic modules-disk
testcd
failsafe

Every time it either hangs right after Tux appears, or when it tries to find the CD drive.
Scanning for USB/Firewire devices... Done.
Enabling DMA acceleration for: hda
Enabling DMA acceleration for: hdc
Looking for CDROM in: /dev/scd0

(Isn't that a scsi CD device? I told it noscsi)
At that point the laptop sits there with the CDROM spinning away and it never progresses. On my other machine (Tower) it only makes it to Tux and never gets to scanning.

I've seen several others with similar issues, but haven't found a consistent answer.
Laptop is an HP 4100 Omnibook, in somewhat clunky condition
Tower is an ASUS CUV4X-E, 512MB Crucial memory (I ran memtest86 and found no errors in RAM)