Change to linux you can have it for free, it does everything most do on MS-W, with security built into the system.
Free to add regularly updated applications for anti-virus and more-devious things
Summary: Antivirus Toolkit
Description:
ClamAV is an open source (GPL) antivirus engine designed for detecting
Trojans, viruses, malware and other malicious threats. It is the de
facto standard for mail gateway scanning. It provides a high
performance mutli-threaded scanning daemon, command line utilities for
on demand file scanning, and an intelligent tool for automatic
signature updates. The core ClamAV library provides numerous file
format detection mechanisms, file unpacking support, archive support,
and multiple signature languages for detecting threats.
rkhunter
Summary: Rootkit Hunter Scans for Rootkits, Backdoors, and Local Exploits
Description:
Rootkit Hunter scans files and systems for known and unknown rootkits,
backdoors, and sniffers. The package contains one shell script, a few
text-based databases, and optional Perl modules. This tool scans for
rootkits, backdoors, and local exploits by running tests like:
* Comparing MD5 hashes
* Looking for default files used by rootkits
* Checking for wrong file permissions for binaries
* Looking for suspected strings in LKM and KLD modules
* Looking for hidden files
* Optionally scanning within plain text and binary files
* Checking software versions
* Testing applications