Porting to Windows
 

I downloaded a VST plugin called LegaSynth (Linux), and I use Windows. What do I need to change in the source to make it run?

You would have to change all the OS dependant functions, of course. Effort depends
on which type of funtionality you're using. A lot of *NIX API can be found in Win32
too (MS has, of course, not stolen them. They've been inspired by *NIX), for
example both Linux and Windows are using Berkeley sockets, so you'll find recv and
the like under both OSses.
Threading APIs show some basic similarities (Windows:_beginthread(void*, unsigned long, void*), Linux: int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
void *(*start_routine)(void*), void *arg), while Process APIs are totally different.
And there are no similarities if it comes to GUI or graphics programming (although there
are some libs under *NIX which somehow resemble DirectX APIs, like SDL).
You probably won't get far if you don't understand what the code is doing. You can't
port with search and replace text editing.
In other words: If you aren't experienced in porting from one OS to another, and if you don't have plenty of time (weeks, months, maybe years) to get into it, or plenty of
money to buy someone else to do it, leave it. If you really can't live without this
software, get yourself a second machine with windows on it instead.

You should take a look at Cygwin. It gives you a Linux-like environment under Windows, and has most of the standard tools and libraries you would find in Linux. It can make porting Linux apps to Windows a lot easier...