On Debian Lenny, it appears that modeline is off by default in vim.
You can put the following in your local .vimrc to enable:
modelines=2 appears to be the number of lines from the top of file to scan for modelines.
Then put this on the 2nd line of your source:
# vim: syntax=perl
You can manually set the syntax scheme in the vim session with
Links for more info: