What person or organization is behind the fastseeker.net website? Is
there a contact address or e-mail address for them?

Hello bytebak:
You must be understandably upset about fastseeker.net.  I am assuming
that the reason is that fastseeker.net have somehow manipulated your
computer so that the homepage of your web browser is set to its site. 
This tactic is similar to the one that lop.com employed, bringing woes
to countless of web surfers.

A quick whois search on whoisreport.com reveals the contact
information for fastseeker.net:

Eagle Logic Inf.  
   Condominio Parque Dom Henrique II - Quadra B - Rua Lorena 185 
   Cotia, Sao Paulo 06716300 
   BR 
 
   Domain Name: FASTSEEKER.NET 
 
   Administrative Contact: 
        Eagle Logic    admin@eaglelogic.net 
        Eagle Logic Inf. 
        Condominio Parque Dom Henrique II - Quadra B - Rua Lorena 185
        Cotia, SP 06716300 
        BR 
        Phone: 55-11-46161213  
        Fax: 55-11-46161213 
   Technical Contact: 
        Eagle Logic  admin@eaglelogic.net 
        Eagle Logic Inf. 
        Condominio Parque Dom Henrique II - Quadra B - Rua Lorena 185
        Cotia, SP 06716300 
        BR 
        Phone: 55-11-46161213  
        Fax: 55-11-46161213 
Source: http://www.whoisreport.com/fastseeker.net

This company is apparently based in Brazil.  Using ping, a utility
present in most computers, I found that its IP address is
216.130.177.240, indicating that it is being hosted by
http://www.webair.com, a web hosting company.  Webair's contact
information is:

WEBAIR INTERNET DEVELOPMENT INC (WEBAIR4-DOM) 
   116 E Fairview Ave. 
   Valley Stream, NY 11580 
   US 
 
   Domain Name: WEBAIR.COM 
 
   Administrative Contact, Technical Contact: 
      Christopher, Michael  (MC9034)                     
domains@WEBAIR.COM
      Webair 
      40 East Merrick Rd. Suite 110 
      Valley Stream, NY  11580 
      US 
      (516) 256-0821 
 
   Record expires on 24-Feb-2005. 
   Record created on 24-Feb-1999. 
   Database last updated on 24-Aug-2002 18:54:24 EDT. 
Source: http://www.whoisreport.com/webair.com

If you decide to complain to fastseeker.net directly, I doubt that
they would care about what you have to say given their business
tactics.  However, you might have better luck if you complain to
WebAir about FastSeeker's practices.

A great freeware called AdAware available at
http://www.lavasoftusa.com might be able to help you remove residuals
from fastseeker.net if it had made changes to your computer.

If you need clarification, please request for it before rating this
answer.
Good luck,
secret901-ga

Search strategy:
"Reverse IP lookup"
"Domain WHOIS"
In addition, I also used ping, a utility available on all Windows
computers.

This is terrific - answers my question exactly and then goes on to
anticipate follow-on questions. Well done.

The registry will contain changes from fastseeker. I've also had my
home page changed and my registry upset by a number of companies.
Yahoo is the most invasive. I've spent hours editing the registry to
undo their damage. First, you can do a registry trick to keep your
homepage so that no one site can alter it. lava will pick up most, but
not all of the changes in the registry. You can search the registry
and delete all of netseekers alterations by doing a "find" search
under Start/Run/Regedit . Right click and you'll get the "find"
feature. Delete all of netseekers entries. Disclaimer: Editing the
registry is at your own risk, you can cause serious problems and may
need to reinstall your O/S.