$values['address'] = "index.php?module=mymod&action=view_in_small_window";
$values['label'] = 'Click on me to open window';

echo javascript('open_window', $values);

Other variables
----------------
Default listed first

toolbar    = no/yes
menubar    = no/yes
location   = no/yes
scrollbars = yes/no
resizable  = yes/no
width      = 400
height     = 300
titlebar   = no/yes
link_title = ''
type       = link/button (default link)