With a good firewall and AV, you will be fine.
You should start off with an anti-virus, and i would suggest you download Avira AntiVir which is available at http://www.free-av.com/en/download/1/avira..._antivirus.html
I would then suggest you use a firewall, and i would recommend Comodo, which is available at http://www.personalfirewall.comodo.com/dow...d_firewall.html
As for anti-spyware/adware/malware i would suggest you download Spyware Terminator, which includes a free real-time shield which is as good as any product you must pay for, and you can integrate ClamAV into the real-time and Scan engine... and its very customizable.
With Malwarebytes anti-malware for a on-demand scanner and you should scan with Avira, ST, and MBAM once every 10 days.
Spyware Terminator : http://dnl.spywareterminator.com/dnl/confi...nator_Setup.exe
Malwarebytes anti-malware : http://www.download.com/Malwarebytes-Anti-...&tag=button
You may also wish to do a monthly scan with an online scanner, and i would recommend NOD32 as it is the second best product of its kind this year... you can find it at http://www.eset.com/onlinescan/
(Internet Explorer ONLY). Ensure you tick the 'Remove found threats' and the 'remove unwanted applications' boxes before starting the scan.
If there's anything I've missed, or any questions then please feel free to contact me
You can view how to turn on the real-time protection for ST at http://www.spywareterminator.com/support/h...od=HELP_Tips_ST
although it is for 2.3 instead of 2.5 of the program.