Blimey!! The poor fella will be sitting there scratching his head at this. There is conflicting advice in every post here!!
G-MANN, this is what I would do, me being a basic computer user.......
1- Download Spybot
2-Download Adaware
3-Download Zone Alarm(Free version)
4-Install all three programmes.
5-Connect to the internet and update all programmes.
6-When updated, run Spybot then Adaware.
7-Update your anti-virus definitions and run scan your computer.
8-Stop looking at dodgy sites!!!!
All of the above will not take more than an hour or so and should be straight forward to do, even for a beginner, don't be put off by all of this, it is easy and very straightforward.
Hopefully, this will sort it out without taking to drastic measures such as reformatting your hard drive as this can sometimes be a pain to do(see posts above) if you do not know much about computers. This is a run down of the basic things you need to do to get rid of problems. If successful, simply keep updating them and you should be ok.
As said earlier, hijack this is the way to go if what I have suggested fails but that is something I know nothing about so will leave that kind of advice to the experts here.
Keep us informed here on what you do to sort it out.
Good luck!!