BSOD Error Need HELP!

Hi
I am asking for a friend who keeps getting the BSOD several times a day. He has read all over the web for answers and there seems to be conflicting advice.

Here is the info I have:
KMIXER.sys STOP:0x00000050 PAGE_FAULT_IN_NONPAGED_AREA

Some posts for Win2000 say to Disable BIOS memory options such as caching or shadowing. Others say it is probably not going to help. Another one said to set BIOS back to defaults (not sure I can walk him thru the BIOS without being there in person)
I read that KMIXER may have to do with soundcard but not sure.
Other posts tell me it is memory.
His is an older computer running WIN XP SP3 He has 3 sticks of RAM 2 512kb and 1 1gb. Does the seating influence this? He has it 512, 1gb, 512.
Could this error be from overheating?
He hasn't installed any hardware and probably not any software that he remembers. This has been going on for about 2 weeks.
Any help would be appreciated.
Thanks