I intend to install Virtual PC so I can use a few Pc programs that I need.

I have been warned that I open myself to the possibilities of virusses. Is it true?

What virus protection should I use for Mac?

The way I understand the procedure to go is that Virtual
PC itself is only a platform emulator (hence the reason
why you can buy it alone if you already own Windows).
You then install a legal, licenced copy of Windows on top
of that emulator. That is the software that will be affected
by any viruses and/or malware. In a worse-case scenario,
you can just trash all Virtual PC related items and reinstall.
That is a tedious process so if you want to buy virus
protection get a windows-based application to install
within Virtual PC. Norton Antivirus and McAfee's software
are the two industry leaders so they are always a good
choice.

Good luck!