In your situation I would go with a hardware VPN solution. This box would maintain your VPN as long as you have internet connectivity on both sides.
I use Sonicwall’s TZ150 for this and seems to just work. A set it and forget type of situation. If you want to do it for free you can use the built in windows 2003 vpn capability. But you will have to manually restart the connections and should have a little knowledge regarding networking and vpn’s.
<a href=”http://www.sonicwall.com”>The sonicwall home page is here </a>and <a href=”http://www.sonicwall.com/us/products/TZ_Series.html”>here is the product page for the one I use here</a>
I<a href=”http://www.nextag.com/Sonicwall-TZ-150-Internet-67732741/prices-html”> found them as low as $218 per box here on next tag</a>
You can also look at the Linksys <a href=”http://www.linksys.com/servlet/Satellite?c=L_Product_C2&childpagename=US%2FLayout&cid=1115416833192&pagename=Linksys%2FCommon%2FVisitorWrapper&lid=3319254480B02″>RV042 </a> at about $180 US each.