It's my understanding that after Walter, we go to Alpha, Beta, Gamma, Delta, Epsilon, etc. but I'm not too sure about that. Only in 1933 have we reached the 'W' storm. Even in 1995 we only had Hurricane Tanya. But who knows? This is one active season.
Here's all you need to know about hurricane naming: http://www.nhc.noaa.gov/aboutnames.shtml