Just a brief revelation to share with any readers (perhaps they stumble here through Google, or by some horrible accident :).
I’ve had an Abit IP35-E motherboard in my HTPC setup for six months now, and while a great overclocking board, stable and packed with nice features (yeah, right, this is the budget version), I haven’t been able to coerce my Debian Lenny installation copied from previous IDE hard drive, or any Linux Live-CD to properly recognize my 500GB Samsung SATA hard drive.
Because booting to Linux rebooted with USB keyboard on, and IRQ options sometimes seemed to work their magic and temporarily get me to login prompt, I figured there was some IRQ conflict at work. I searched for the fix just half a year ago with no luck, but after 5 months of complete Linux abstince (spelled that wrong, I did), I stumbled upon an article in (now defunct) Fatwallet.
Turns out all I needed was to swap SATA cable from SATA1 port to SATA5 to avoid IRQ conflicts. Voila, now everything works great, no IRQ conflicts there (only SATA1-SATA4 ports conflict with USB controller).
Hope this helps someone!