variant of Win32/injector.BQ trojan >> HELP!

I'm running Vista Ultimate 32 Service Pack-1 with all the
Windows updates, also Windows Defender and
NOD32 antivirus, all up to date and always running. Even so
I got a variant of Win32/injector.BQ Trojan.
Now every time I try to browse a web site or even when
opening a folder a warning pops up that reads:

" you machine is infected with a virus and you should perform
a free virus scan.then a NOD32 warning appears saying:

----------------------------------------------------------------------------------
http://free-viruscan.com/00/00/00/error.php

Description:

Access to the web page was blocked by ESET NOD32 Antivirus.
The web page is on the list of websites with potentially dangerous
content.
---------------------------------------------------------------------------

It seems that NOD32 caught this, but my machine is already infected
as no matter what I do I can't get rid of the problem.

I have performed a full Antivirus and Windows defender scan, also
I installed Search and Destroy and Adaware, and after running these
there were some problems detected and apparently cleaned.but
still the problem.

All mi programs, my e-mail and others are working OK, but I cant
browse the web or open some folders.

Is there a tool to remove this?

I'll appreciate any help regarding this.

Thanks in advance.
Willy

PS: How I got infected when running NOD32, Windows Defender, and
my Windows firewall up and running, should I install a different antivirus?

.