[CentOS] Weird crash with CentOS 5.1

Dear all.

I'm experiencing a weird crash with one of our desktop running CentOS 5.1

We have 5 machines identical, onle one has this problem.

Right after it starts, it will kernel panic. Unfortunately, from the
backtrace this is all I've managed to get : serial port isn't working.
So it's a manual copy of what the screen show.

[<c04721f3>] sync_buffer+0x0/0x33
[<c04bff66>] avc_has_perm+0x3a/0x44
[<c04c055d>] inode_has_perm+0x54
[<f8899829>] ext3_lookup+0x25/0xb7 [ext3]
[<c047b0d1>] do_lookup+0xb4/0x166
[<c047ce5b>] __link_path_walk+0x87a/0xd33
[<c047d35d>] link_path_walk+0x49/0xbd
[<c046f582>] sys_chdir+0x4f/0x57
[<c047d72a>] do_path_lookup+0x20e/0x25e
[<c0470daf>] get_empty_filp+0x99/0x15e
[<c047dfd7>] __path_lookup_intent_open+0x42/0x72
[<c047e056>] path_lookup_open+0xf/0x13
[<c047e15a>] open_namei+0x7b/0x609
[<c046e8ca>] do_filp_open+0x1c/0x31
[<c046f582>] sys_chdir+0x4f/0x57
[<c046e91d>] do_sys_open+0x3e/0xae
[<c046e9ba>] sys_open+0x16/0x18
[<c0404eff>] syscall_call+0x7/0xb
=======================
Code: 0c 29 d0 83 e8 18 c1 e8 03 39 c1 74 29 68 d4 22 8a f8 68 80 01 00 00 68 3e
21 8a f8 68 68 12 8a f8 68 4e 21 8a f8 e8 d0 f1 b8 c7 <0f> 0b 80 01 3e 21 8a f8
83 c4 14 8b 44 24 28 89 44 24 0c 66 8b
EIP: [<f8897626>] dx_probe+0x16e/0x2b4 [ext3] SS:ESP 0068:f7e47cc4
<0>Kernel panic - not syncing: Fatal exception

This machine is dual booting windows and CentOS. Windows has no
problem and will run just fine (so I believe this is not a hardware
issue).
Interestingly, this machine worked fine for several weeks and one day
decided to crash within the first few seconds of boot.
I have tried with several kernel, including the latest one as of
today: not working any better.

If I boot the CentOS DVD, when it comes to searching for existing
CentOS installation, it will crash just the same.

If I format the linux partition, I can then re-install CentOS, update
it just fine... Then a few days later it will crash just the same
right after booting.

This machine is running a Gigabyte P35-DS3P motherboard, with 2GB of
DDR2-667MHz RAM, an Intel core-duo quad: Q6600.
It has two 250GB hard drive in RAID1 using the bios RAID support (so I
can have RAID on both Windows and Linux).
It's running the 32 bits version of CentOS 5

Any ideas what the problem could be?

Any help will be greatly appreciated.

Thank you
Jean-Yves