Virtual folders are always browsable.. or did you mean a Real Folder?
You should then simply use an external comment. To do that, just go to the same folder where the file is located on your hard-drive and create a file that is named exactly the same as the file you want to give a comment, but give it the .comment extension
For example:
if a file is called 'setup.exe' you would have to create a file called 'setup.exe.comment'.
All you have to do then is to open that .comment file in any text editor and write your comment. After ure done, simply save and close the file. Hfs will use the external comment file automatically.