How to mimic the vim 6.0 plugin feature with older versions
From Vim Tips Wiki
created July 5, 2001 · complexity intermediate · author bubbleboy · version 5.7
If you do not have Vim 6.0, but would like to mimic the plugins directory feature then copy and paste this into your vimrc:
exec "source " . substitute(glob($VIM."/plugins/*.vim"), "\n", "\nsource ", "g")
It will automatically source every Vim script file located in the vim/plugins directory.
Now, to add a new plugin, just drop the script in this directory and Vim will automatically find it.
To make Vim look in your home directory for the plugins directory:
Use $HOME, or ~ (tilde), instead of $VIM. If you use tilde, it must be inside the quotes. The $VIM (or $HOME) may be placed inside the quotes as well - glob("$VIM/plugins/*.vim") works just fine.