I would like to read a field (which is an image file name) from the database, build a datagrid with a hyperlink column, and to display those images on a hyperlink click in the separate window.

This is easy. Just need to describe a hyperlink column as

<asp:HyperlinkColumn Target="new" DataNavigateURLField="FileName" DataNavigateURLFormatString="ShowImagePage.aspx/{0}".....

where ShowImagePage.aspx is a new window and
FileName is the database field name.

But I would like to set a specific size while openning a new window (and to make it non-resizeable) like
window.open("ShowImagePage.aspx/{0}",,"width=500,height=500...")

Any ideas how to implement it?