Installation of FC6 fails with a kernel panic, probably due to AGP

[Paso]

Hello there.
As in the subject: I try to install FC6, but the installation fails with 
a kernel panic:


EIP: [<c04140c7>] clear_local_APIC+0x11/0xaf SS:ESP 0068:dfa13588
  <0>kernel panic - not syncing: Attempted to kill init!
  <1>BUG: unable to handle kernel paging request at virtual address ffffd370

[several (to me incomprehensible) text lines]

Call Trace:
  [<c041416a>] disable_local_APIC+0x5/0x29


After some "heuristic" attempts if have found out that if I disable the 
AGP card and use the onboard video card the installation goes on without 
any problem (or at least doesn't stop with the kernel panic... I don't 
perform a complete installation so far... ;-)). Of course this is not a 
feasible solution...

The same problem appears also with previuos releases of Fefora core (in 
fact since FC2, I can install without problems FC1) and with different 
AGP video cards (e.g. ATI Radeon 9200).

I try to boot the installation with "noprobe", "noapic", "headless" and 
many other options, but nothing changes.


My hardware:

Motherboard: AsRocks p4i56GV with
ASRock A.G.I. 8X  - VGA upgrade slot, (AGP8X/4X compatible)

Actual Video Card: Nvidia GeForce 6800 XT (but the problem appears also 
with different cards)


Any suggestion?

Thank you all,

Stefano