HELP! Calling IT Kossacks and Computer Geeks! w/poll

Help all you techie and IT-support Kossack geeks out there!  Please any help you give me will be most appreciated.  I'm a techno-ignorant average Jane who doesn't know how to fix this problem beyond what I've tried so far.  And please be patient with the probably wrong language I use to describe what's happening :-)

Here's the problem:  I click on a site, or try to go to a URL, and instead I get routed to a Gateway page that says it can't find this:

(below the fold)

htt:://ad.doubleclick.net/adi/N3671.YahooNetwork/B2627719.18%3Bsz

I'll click on earthlink, and get the above message.  I'll click on eBay, and get the message.  Or I'll be within a site, like google, and get this message.  It doesn't happen 100% of the time, and is solved by my restarting the computer.  But then gradually a message like that comes back and it seems I can't get anywhere.

I suspect this is spyware but I don't know how to get rid of it.  I've installed Spyware doctor, and done microsoft malware remover scans.  I've got Trend Microsystems antivirus installed.  Can anyone tell me very clearly and in layman's terms step by step what I have to do to get this bug out of my computer?

THANK YOU!!!!!!!!!!!!!