There are way too many connections on a default Windows system and since Windows is closed source, you cannot fully trust it to not establish any other connections.

I have 2 simple ideas:

1- The easiest and should be used regardless of any additional firewalls: Use PeerBlock. Simply create three lists, one for blocking all IPs with a single 0.0.0.0-255.255.255.255 range. The other two will be for allowing connections, one for a Tor relay list, the other for other whitelisted IPs that you prefer or which are required for internet connection.

2- Use a physical or virtual router to whitelist Tor IPs while blocking everything else. I would suggest a cheap physical router that you can install an open source firmware. The other idea is to have a virtual router which I didn't try because it would still not be secure (closed-source Windows) and it would require more system resources. Here is a tutorial which could work: http://timita.org/wordpress/2011/07/29/protect-your-windows-laptop-with-pfsense-and-virtualbox-part-1-preamble/

In order to whitelist Tor IPs, there are some websites providing Tor relay lists. You may need to use other tools to convert these lists to be used on PeerBlock or on your router. Also, you may have to regularly update your lists, though it would work a long time without updates.

There are way too many connections on a default Windows system and since Windows is closed source, you cannot fully trust it to not establish any other connections.

I have 2 simple ideas:

1. The easiest and should be used regardless of any additional firewalls: Use PeerBlock. Simply create three lists, one for blocking all IPs with a single 0.0.0.0-255.255.255.255 range. The other two will be for allowing connections, one for a Tor relay list, the other for other whitelisted IPs that you prefer or which are required for internet connection.
2. Use a physical or virtual router to whitelist Tor IPs while blocking everything else. I would suggest a cheap physical router that you can install an open source firmware. The other idea is to have a virtual router which I didn't try because it would still not be secure (closed-source Windows) and it would require more system resources. Here is a tutorial which could work: http://timita.org/wordpress/2011/07/29/protect-your-windows-laptop-with-pfsense-and-virtualbox-part-1-preamble/

In order to whitelist Tor IPs, there are some websites providing Tor relay lists. You may need to use other tools to convert these lists to be used on PeerBlock or on your router. Also, you may have to regularly update your lists, though it would work a long time without updates.