I wanted to use the vim for editing the processing files and while looking for a way to have syntax highlighting I found that a lot of people have trouble with that and that there is an easy way to get it.
Just add this line to your .vimrc:
au BufRead,BufNewFile *.pde setf java
As processing is basically java, this uses the built in java syntax highlighting which works just fine for me :-)
If you do not have syntax highlighting enabled use this line in the .vimrc to enable it: