Using the Antivirus Application: Your best helper is the antivirus program on your computer. Keep it always updated. Install another freeware application if your antivirus has expired or is not upto your expectation. Anyway you can keep the antivirus on your computer and also install another one. I will tell you how to . I have been successfully using the Avast Home Edition Antivirus installation to remove most of the infections. You can choose from Avira, Avast and Avg, all three provide a free version of their antivirus software. 

Here is what you need to do. Open the system configuration utility. Click on start > run , type msconfig, press ok, select the startup tab, expand the middle column, locate the entry of your antivirus application, and uncheck it, press apply, press OK/Close, Exit without restarting. Now Download and install the Avast Antivirus Home edition from avast website. Keep your computer connected to internet so that it can update itself during installation. Run the installer, selet the option to "Schedule a boot scan during startup", now it will prompt you to restart the computer. During the boot scan, it will detect the viruses an prompt you for action, select delet/delete All, as you see appropriate. Let it complete the scan and start your computer.

once the viruses are removed you can uninstall Avast antivirus, if you decide to stick with your antivirus. In that case, go to startup and check the box of your antivirus in the list, press apply, press ok/close and restart the computer.
If you decide to keep Avast and your antivirus both together, keep only one entry checked in the startup list, so that only one antivirus is active at any given time. You can use the other antivirus whenever you want, simply by turning off the running antivirus and then opening the other one. As long as you run one antivirus at a time, you can have as many antivirus programs on your computer as you want.
If you decide to use Avast alone, you can uninstall your antivirus application, if it was a demo version, or a commercial version which is not updating anymore because you have not paid for the yearly subscription, in that case it is better to uninstall the antivirus.

If you decide to keep Avast Home edition antivirus, do not forget to fill in the registration form on their website, on the same page where you downloaded it. You need to fill in your email ID, avast will mail you the product activtion key. The activation lasts for one year, and can be updated for free again. I have been using it since more than a year now, and it has been good so far. 

Avira Antivir Peronal : provides protection against viruses, worms and Trojans, dialers, includes Anti-rootkits, and Antifishing. It is known to have the  best detection rate among freewares. visit Avira website

Avast Antivirus Home Edition: It has all of the above and additioally it provides protection for Nework, Web, P2P, Internet mail etc. Each one has a separate shield, which can be turned On/Off according to your requirement. Needs to fill in the registration form to get one year's free license. Visit Avast website

AVG Free Antivirus :  It is perhaps the most popular antivirus. It requires less ram memory to function, therefore it is popular on computers with less RAM. It won't bog down your computer the way Norton does.  It includes an Antispyware as well. But the detection rate is poor among these freeware antiviruses. Visit AVG website