Dude I fought with that bewitched sp.html & sp.htm about blank hijacking problem for months. Hijack this and adaware would get rid of it only temporarily.
 
I ran this tool and it is completely gone. It has been well over a week and no problems.
 
http://securityresponse.symantec.com/avcenter/FxAgentB.exe
 
they have some instructions for running it here.
 
http://securityresponse.symantec.com/avcenter/venc/data/backdoor.agent.b.removal.tool.html
 
Hope you have success. I know this also worked for one other guy. Yet another guy ran it and it did not work for him.
 
I would delete all your temp files and run spyware tools first.
 
leave a post here if it works.