You need JavaScript for that...
Yould make an image 'container' page in asp that takes in a parameter
from the url that tells it which image to load.
Dim image
image=Request.QueryString('img')
Response.Write("<img src='"&image&"' alt='Big Image' />")
To open the page you just need something like:
<a href="image.asp?img=path_to_pic.gif" onclick="return !window.open(this.href, 'image_window', 'width=400,height=400');">
<img src="path_to_thumbnail.gif" alt="Thumbnail" style="border-style:none;" />
</a>
HTH,
--47.