are macs susceptible to any kind of virus or spyware if i were to bring in the element of using a program like Parallels (recreates windows environment to run windows oriented files like .exes) or a Windows VPS?
Well, let's clear up one thing - Macs are not impervious to Malware (which is actually a category of software, that comprises viruses, spyware, trojans, etc). A lot of people confuse the term "virus" with "malware". While it's true that there are no self-replicating viruses for the Mac (yet), there are a few trojans and adware that can be just as much of a pain in the rear.
Windows is still Windows, even when it's running on a Mac. So, you'll definitely want some kind of anti-virus installed on Windows. For most people, Microsoft's own Security Essentials works well.
which would be the 100% safest option in protecting myself if i were to run a custom .EXE file from my MAC....
There is no 100% safest way to do anything on a computer that involves third party software. There are general "common sense" guidelines, which have been covered elsewhere in this thread, but few things in life are 100%
running it thru a windows vps?
or running it thru a virtual pc program like Parallels?
I don't know what you mean by "vps". Parallels, VMWare Fusion, Virtualbox, etc simply allow you to run a "guest" OS inside of a host. If you're really worried about some kind of malware writing to your Mac's partition, then you can disable the sharing of host folders, but honestly, the chances of a Windows malady actually doing something destructive in that fashion are slim to none.
Boot Camp may afford you a little more protection since Windows can't write to the Mac's partition without the help of 3rd party software.
would i still need to install any kind of spyware, virus software if i were to run it in parallels?
Any way you run Windows, you'll need an anti-virus product of some sort. There's just far too many Windows-specific malware in the wild.