several stop errors - sudden crashes! can anyone help?!

hi!
when working on my computer, windows xp pro suddenly crashes. no blue screeens or error messages appear. the eventmanager lists severeal stop codes without any error descriptions:

0x000000c2 (0x00000007, 0x00000cd4, 0x00005e26, 0x85c2e430).
0x100000c5 (0x00000000, 0x00000002, 0x00000001, 0x80543803).
0x1000000a (0x0a070007, 0x00000002, 0x00000000, 0x805001ad)
0x000000c4 (0x00001005, 0x8d9a6fdc, 0x85b65810, 0x00000000).

i searched the whole internet, and a lot of people have had the same problem, but none of those solutions would work for me!
it would be very kind if one of you guys could analyze my minidumps and tell me what the exact problem is. i ran memtest, tried installing new drivers, switched ram positions, installed new os... please help me!
i have attached 6 minidumps!
thanks, felix

Hi, your crashes are caused by a few things, avg7rsw.sys a file in AVG Anti-Virus, FILTNT.SYS a file in Outpost Firewall and USBPORT.SYS. Read this to hopefully get rid of the USBPORT.SYS crash http://support.microsoft.com/?kbid=822603 As far as the other crashes I would uninstall the firewall and Antivirus programs (while in safe mode) and use another Anti-virus program and software firewall. Also if you have more than one Anti-Virus program on the computer, that could cause the crash as well.

thx for the quick response.
i have already thought that it might have sth. to do with either avg or outpost. i dont understand it though. but the problem has appeared when i used outpost and avg for the first time, earlier on is used the whole norton suite. i wanna ged rid of norton and i liked avg n outpost. at least everything works fine with the norton products installed. btw, any recommendations which free antivirus and firewall to use?!
again, thx for ur help!
felix

I used Avast Anti-Virus: http://www.avast.com/eng/download-avast-home.html
and Sygate Personal Firewall and they worked great and played well together.
http://www.tucows.com/preview/213160