[SMTP] How do I check for faked header info?

I need to know this as I got an e-mail from my ISP telling my I've got a Proxy virus, which is virutally impossible as I'm the only one who can install anything, change anything etc. on this computer and the damn thing is firewalled as well as equipped with an up-to-date version of NAV2004.
the mail originated, according to Outlook 2002, from NOREPLY@cHELLO.NL, had a 244B .txt attachment that had as name "Norton Antivirus 2004 is uninstalled!.txt" which is fishy in my book.
Also my ISP doesn't give any Proxy-virus infected users any respite, they shut you off and then notify you, also, if you HAVE been infected AND lucky enough to have been given some respite (a week orso) you get an e-mail from Abuse@, so I know this isn't for real. Too bad my dad think otherwise.
So, question is, how do I check whether or not the SMTP Header info is faked, and if possible, how do I check for the real sender so I can report him/her/it to the abuse dept of my ISP ?

 

maybe this might help
http://www.stopspam.org/email/headers.html

 

thanks all, sent a mail to my ISP's abuse dept about this