BB> This company, DC Teknology!! (http://www.dctek.ca),
 BB> sends me ads for computer products on a regular basis.
 BB> I have tried once to be removed. I want to email his
 BB> ISP that he is sending SPAM. The header of the message
 BB> is below, how do I determine the email address to use?

i processed the header that you posted and came up with the following...
what you do with the info is up to you ;)

**********
Parsing:
Sender (or dispatching mailserver) IP:209.226.175.101
He/she/it has said to be :tomts27-srv.bellnexxia.net
Receiving mailserver [by]:TROUT.internal.nexusds.com
**********
Parsing:
Sender (or dispatching mailserver) IP:67.71.2.110
He/she/it has said to be :retail.dctek.ca
Receiving mailserver [by]:tomts27-srv.bellnexxia.net
The trusting level of this Received line: is 25%
Listed in:
*  bl.spamcop.net
67.71.2.110 is a known spam source
***** RESULTS ******
- 67.71.2.110([No rDns configured]): Spam source
OrgName:    Bell Canada
OrgID:      LINX
Address:
City:       Toronto
StateProv:  ON
PostalCode: K1G-3J4
Country:    CA

NetRange:   67.68.0.0 - 67.71.255.255
CIDR:       67.68.0.0/14
NetName:    BELLNEXXIA-11
NetHandle:  NET-67-68-0-0-1
Parent:     NET-67-0-0-0-0
NetType:    Direct Allocation
NameServer: NS3.BELLGLOBAL.COM
NameServer: NS4.BELLGLOBAL.COM
Comment:    ADDRESSES WITHIN THIS BLOCK ARE NON-PORTABLE
RegDate:    2002-04-18
Updated:    2003-07-24

TechHandle: MK1209-ARIN
TechName:   Khalid, Mohammad
TechPhone:  +1-800-450-7771
TechEmail:  noc{at}in.bell.ca

OrgTechHandle: SYSAD1-ARIN
OrgTechName:   SYS ADMIN
OrgTechPhone:  +1-800-565-0567
OrgTechEmail:  ip_prov{at}bellglobal.com

# ARIN WHOIS database, last updated 2004-07-13 19:10
# Enter ? for additional hints on searching ARIN's WHOIS database.

CustName:   Bell Sympatico
Address:    21 Caniff Street
City:       Toronto
StateProv:  ON
PostalCode: M5V-3G1
Country:    CA
RegDate:    2003-10-21
Updated:    2003-10-21

NetRange:   67.71.0.0 - 67.71.3.255
CIDR:       67.71.0.0/22
NetName:    BELA1021-CA
NetHandle:  NET-67-71-0-0-1
Parent:     NET-67-68-0-0-1
NetType:    Reassigned
Comment:    LINX
RegDate:    2003-10-21
Updated:    2003-10-21

TechHandle: MK1209-ARIN
TechName:   Khalid, Mohammad
TechPhone:  +1-800-450-7771
TechEmail:  noc{at}in.bell.ca

OrgTechHandle: SYSAD1-ARIN
OrgTechName:   SYS ADMIN
OrgTechPhone:  +1-800-565-0567
OrgTechEmail:  ip_prov{at}bellglobal.com

# ARIN WHOIS database, last updated 2004-07-13 19:10
# Enter ? for additional hints on searching ARIN's WHOIS database.

* Begin abuse addresses'extraction details *
Possible abuse found using whois contact info: noc{at}in.bell.ca
Possible abuse found using whois contact info: ip_prov{at}bellglobal.com
* End abuse addresses' extraction details *

Possible abuse address: ip_prov{at}bellglobal.com
Possible abuse address: noc{at}in.bell.ca