I understand in a way what you've gone through. Spyware and trojans are not very nice at all! They're also a bitch to remove, too!
It sounds like your IE
browser's been hijacked so that it ends up with that .html file as the new homepage. While Hijack This does well at removing unwanted files, have you also considered that you Favorites section of your IE
browser might still have that c:searchpage.html inside it? If so, just right click on it and delete it, then remove it using Hijack This.
Also, have you checked through Internet Options (under Tools on your IE
browser) and checked what the homepage's been set to? If it's that .html file, just delete it and put in whatever URL your regular homepage is. Then check with Hijack This as well.
I have Hijack This on my 'puter and all those anti-spyware stuff abovementioned too, and I've been through a similar thing as you have, with the unwanted file stubbornly refusing to be removed at first.
As for the regedit thing, I'm not entirely sure what it means to modify the keys to an empty string. Besides, in my regedit, there is no such string. I guess it's because my OE is not set up in the same way or is a different version. (I have OE 6 and IE
I'm no expert on regedit, but as you probably already know, regedit's not something to be fooled around with.