[ILUG] VIM "on the fly" syntax checking?

[Justin Mason]

Hey ILUG --

Quite a few IDEs nowadays offer the option of quietly running syntax
checks "in the background", while you edit a document.   For example, if
I'm writing code and insert a syntax error, it'll report the error *while
I'm editing*, without me having to hit a key to trigger a build macro or
the like.

Does anyone know of a way to do this in VIM?

(I know it's possible to have the syntax highlighting highlight errors
that *it* can detect.  That's great, but I want more ;)  I'm looking for
some way to trigger a build in a subprocess, capture the errors, and
display them -- without interfering with ongoing editing in the
foreground.)

--j.