Spyware is driving me nuts

[b2tf]

Ok, ive hit a brick wall with this so i hope someone can help.

I have no idea how i got it on here in the first place, but my computer is seemingly laced with spyware, in particular some stuff called 'iSearch'. Ive used Adaware, Norton and Spybot, as well as one called 'Webroot Spy Sweeper', and it kills it off ok, the trouble is it keeps on bloody coming back.

This iSearch stuff keeps on redirecting any website i open to its own page, and im finding about 10 applications that i didnt run wanting to connect to the Internet (luckily ZoneAlarm is stopping them though). Im also getting links appearing in just words on the forum (i.e. someone's posts contains links in it which i know are not supposed to be there).

Norton is up to date as of 10 minutes ago and is not finding anything, so does anyone have any suggestions as to what i can do to kill this crap off once and for all? I think ive used just about every adware killer known to man and its just not budging.