For finding abuse addresses for known domain names go to
http://www.abuse.net and enter the domain name in the search box, this should give you the abusemaster's e-mail address for complaints about hacking/virus infection/offensive e-mails/spamming and other non-acceptable behaviour.
Another useful place to find out about domains, reverse IP lookups, etc. is the Sam Spade site. This is a domain name search engine and can be found here:
http://www.samspade.orgAnd another really handy site is the Robtext swiss army knife internet tool website here:
http://www.robtex.com/In the UK the Internet registry can be searched for UK domains only here:
http://www.nominet.org.uk