First of all, there's a difference between some redirecting adware trojan and a virus, sometimes not a lot but still.
Use the "Adaware" free version of just about any adware software, most are good. Use a firewall too. ZoneAlarm has a good free one.
Use AVG free version for anti-virus protection. All three of these work well together, but that can't be said for many others--they just don't play well together sometimes. Norton is one of the worst, and McAfee too.
More of the problems occuring with having a "redirect" installed come from browsing habits (don't "Bop Bonzo") or email opening habits (don't allow it to open outside links or pics) ...and I.E., usually, installed with default settings of "install on demand" and a couple of others set for "on". (like having strange icons pop up on your desktop sometimes?)
There are folks out there that will take advantage of you on the internet---as if ya didn't know that.
Using Mozilla or Firefox browser will help some. Using an different email client wouldn't hurt either--use Thunderbird (or mozilla email).
Even better yet--switch to using one of the Linux distro's and forget using Windows as much as ya can. It is very possible to dual boot with Linux and Windoze both installed on the hard drive.
The "House Call" online service should be free and is fairly good.
Forget buying or paying for a service, the free versions work as well and are updated as frequently.
And here's probably one of the best places to get help with various problems you could find...and it's mostly free stuff...and good advice.
http://www.tomcoyote.org/hjt/Read a lot there, use the software--it's good stuff. And if they can't help ya get the problem fixed---there might not be any hope at all. Very knowledgable folks hang out there. There is only one (that I am aware of) trojan redirecting $%%$ thing that embeds itself into the very networking of windows that can't be removed without a complete reinstall....the other stuff can be scrubbed out.
Virus's are another matter, however.