application error

I don't know if this is the right forum for this problem. My apologies if it is not.
I have a Dell Inspiron E1705 running Windows XP pro which I purchased in
May 2006. I typically use Firefox as my browser. For the last couple
of months, I have been getting frequent pop-ups that say:

"[SOFTWARE] Application Error "
"The instruction at <ADDRESS> referenced memory at <ADDRESS>. The
memory could not be "read". Click ok to terminate this program."

The messages reference many different software packages that I run,
including:

IEXPLORE.EXE (even when I'm not running Explorer)
MCUPDATE.EXE
XPCOM: Event Receiver: Firefox.exe
FFHOOK: firefox.exe
DSBrws.exe
itunes.exe
MCINFO.EXE
ADOBEACROBAT:ACRORD32.EXE

I have run Sunbelt Counterspy and PC tools Spy Doctor to check for spyware and Registry Mechanic and RegCure to clean the registry, but nothing seems to help.
In various tech forums, I have seen many people with similar problems, although typically they receive messages in reference to only 1 software package whereas I seem to receive them for many.
I would appreciate any ideas? Thanks in advance for any help.
zoe36