Registery protection I use - Spybot, (enable the resident protection)
Firewall use - Zone alarm
Bot checker I use - Adaware
Virus checker I use an online one but there are probably many
http://housecall.trendmicro.com/uk/
All these are free, also be carefull use common sence and keep the microsofts updates up to date
If I get any issues that cant be fixed I just recover from a backup using Acronis, does a full re instal in about 30 mins