Vista - Blue Screen - Page fault in non page area

Hi

I keep getting a problem which appears to happen randomly, every so often
the computer will peform a physical memory dump and hold the warning message
'Page Fault in Non Page Area.' As i said, it appears random and i thought it
may be something to do with memory - i have 2 gigs of ram as 2 sticks. I took
each out and put them in each ram port and still came up with the same
message.

I got a problem signature of:-

Problem signature:
Problem Event Name: BlueScreen
OS Version: 6.0.6000.2.0.0.768.3
Locale ID: 2057
Additional information about the problem:
BCCode: 50
BCP1: FFFFF98406AAB024
BCP2: 0000000000000000
BCP3: FFFFF80001E71101
BCP4: 0000000000000005
OS Version: 6_0_6000
Service Pack: 0_0
Product: 768_1
Files that help describe the problem:
C:\Windows\Minidump\Mini072208-15.dmp
C:\Users\Greg\AppData\Local\Temp\WER-52790-0.sysdata.xml
C:\Users\Greg\AppData\Local\Temp\WER3CFF.tmp.version.txt

I really have no idea of what is causing the porblem and would like any
advice if possible on fixing it preferrably without buying anymore hardware!
But i understand to fix it i may well need to be.

My PC Specs are as follows:-

2.40 quad processor
2 gb ram
256 mb graphics card
Windows Vista 64 bit...

Hope for any solutions possible.

Thanks for your time.

Greg