Correct. Windows only software (malware, most viruses, etc) will still run only on windows. You could have an infected Windows file (for example, a .exe executable) sitting on your OS X partition, but OS X would remain uninfected, as windows binaries will NOT run on OS X, regardless of your hardware platform. To date, there are no viruses or malware that are able to cross over from a windows install on the same system as OS X. I wouldn't expect to see anything like this any time soon, if ever (it would be extremely difficult, if even possible at all). Of course, as always when dealing with windows, be safe. Use Firefox or Opera, Antivirus protection, and scan for malware/spyware periodically with a program like Spybot Search & Destroy.