No, I'd only be transferring files from my OSX to the Windows partition (if that's possible)
Then no, you don't need to worry about viruses.
And yes, it's possible to copy files from the OS X partition to the Windows partition -- depending on your setup.
While OS X can see the Windows partition, you may not be able to copy or save anything to it -- once again, depending on your setup.
To save or copy things onto it from OS X, the format of the partition has to be FAT32 (less than 32 GB). Note that Vista will no longer work with FAT32, so unless you're running XP, this won't work, and you won't be able to save or copy things to Windows from OS X.
However, there are other options. You can download
NTFS-3G which WILL allow OS X to save or copy things to an NTFS partition (larger than 32GB and/or using Vista). It works quite well and gets around the 32GB limit, in addition to getting around the Vista problem. Or, on the Windows side, get a copy of
MacDrive, which will allow you to access your Mac disks while running Windows.