Sorry, I didn't notice that you referred to a popup window.
try:
Code:
<a onclick="javascript: return !popupOpen('login.php');" title="Login to view Special Dealer Pricing" href="http://<your_domain>/login.php">Login to view Special Dealer Pricing</a>
or
Code:
<a onclick="javascript: return !popupOpen('login.php');" title="Login to view Special Dealer Pricing" href="http://<your_domain>/<xcart_root_dir>/login.php">Login to view Special Dealer Pricing</a>