How to check if a virtual directory exists?

I am very new to NSIS am working on my first installer with it. I am stuck at a point where I have to check for the existence of a virtual directory. Is there a way to check if a virtual directory exists without having to create it (and relying on IIS to generate error codes if it exists)?

Yyyyeeeeelllllp...

LangString ERR_VDIREXISTS ${LANG_ENGLISH} "A virtual directory named ${VDIRNAME} already exists. The new virtual directory will not be created."

Go through this page...

Thanks shouman for pointing that out, but that does not solve my problem (or I am unaware of NSIS features to follow it through).

What I need is as follows:
1> Detect if a virtual directory is present
2> If present - continue installation with NSIS script

so my problem is how do i set a variable within the script that indicates the presence or absense of a virtual directory.