In lieu of answering your question, I will give you the choice of the forum pros
Use Microsoft Security Essentials
Malwarebyte
and the Windows Firewall
There has never been a BSOD problem with Essentials, which is not true for most other AV
It uses low resources and is made just for windows.
It is totally compatible with Windows.

Malware is the term used for all but Virus, although a virus is malware, too.
You can use my suggestions together and should
If you want to use Kis it is always best to use the most up to date. Those creeps out there that write these virus and malware, are improving their methods not to be detected. The most up to date software can help fight that problem
Any sort of malware can slow down your computer at best. At worst it can steal your bank password, log your keystrokes and in general spy on you.

KIS is an anti virus and yes it can be used with the free malwarebytes, since the free version is all that is required. Run a scan once a week.

Did I mention that Essentials is free and rated very highly?
http://www.microsoft.com/security_essentials/

If you have any other questions or problems, I would very much like to help