<p>I work with quite a bit of multi-platform C/C++ code, separated by common #defines (#if WIN, #if UNIX, etc).  It would be nice if I could have vim automatically fold the sections I'm currently not interested in when I open a file.  I've searched through the vim script archives, but I haven't found anything useful.  Any suggestions?  Places to start?</p>

Just add a folding region to your syntax
http://vim.wikia.com/wiki/Syntax_folding_of_Vim_scripts#Syntax_definitions
```
```
:syn region myFold start="\#IF" end="\#ENDIF" transparent fold
:syn sync fromstart
:set foldmethod=syntax
```
```