Random startup crashes

[mokawi]

I have no clue whether this will help, but here's what I did before:
I installed Fedora Core 6 with a netinstall, all went fine. Did some tweaking that required some restarts—all went fine. Then I set up internet, which wasn't working well with NetworkManager (somehow, it did work with WEP, but not with WPA-PSK) using this method (which involves writing a init.d script. http://doc.fedora-fr.org/Connexion_W...uration_finale), and since it didn't seem to work perfectly, I deleted the init.d and rc5.d files with rm and went on with this method (http://doc.fedora-fr.org/Configurer_une_connexion_wpa) , which dwells with system-control-network configs to get it to call wpa_supplicant to connect to WPA. I also deleted a wifi0 port that because my machine didn't recognise my network card as it was (an atheros-based f5d7000v5) and added an ath0 port using this method (http://doc.fedora-fr.org/Wifi-Instal...effectu.C3.A9e, see information box). There is still an extra ethernet card in the Material tab, and my wifi card isn't there.
I restarted network service, and it went great. I might have installed other gizmos (music, livna, tcl/tk, abiword, etc) as well, but it's definitly the most dangerous moves I made.
Then I restarted and got my first crash. Since then, my machine only gets to the login screen once in four. The crashes I observed are of three type:
1) Total freeze while the services are loading. The spinning widget stops, and the mouse is frozen. This one is rare; happened only once in the 15-20 reboots I've done ever since. It was loading eth0.
2) A message appears in a terminal fashion on the top of the graphical thing that shows the evolution of the startup process. It usually says something like this (real example):

Vector: 300 (Data Access) at [d275bcc0]
pc: da6816d8: ath_halcomputetxtime+0x10/0x1c8 [ath_hal]
lr: da40b188: calc_usecs_unicast_pacjet+0x184/0x1e8 [ath_rate_sample]
sp: d275bd70
msr: 9032
dar: da77b2da
dsisr: 40000000
curent = 0xd69e98f0
pid= 2434, comm = cupsd
enter ? for help

Sometimes, there's also a message saying that the error is unrecoverable. Vector is often 200 instead of 300, most numbers usually change, as well as pid and process name. The time changes too; it can happen at the beginning or at the end of the service loading. I think pc and lr messages (but not the numbers at the begining) might stay the same, but I haven't checked all the time. Hitting "?" does zilch. It waits for a while, then restarts.
3) Same as preceding, except that the message is repeated again and again every 2 seconds or so. There is no reboot if one waits, it just keeps outputting error messages.

When it reaches the login screen, I'm usually in a safe territory. No kernel panic, no freeze, only the usual occasional application crashes.

Thanks a lot for your help, it is very appreciated.