Different SVN Server versions and Clients

We are going to migrate from CVS to SVN using Subversion 1.6. But also we have another SVN-Server using Subversion 1.2 (no chance to update). So we plan to use the newer TortoiseSVN 1.6.x

Is it possible to use two different servers while using only the new TortoiseSVN?

Another solution may be using an old TortoiseSVN compiled against Subversion 1.2. Is this possible?

What about using two TortoiseSVN (1.2.x and 1.6.x)?

Is it possible to use two different servers while using only the new TortoiseSVN?

Yes, you can use new TortoiseSVN with old server. Quoting Subversion FAQ:

The client and server are designed to work as long as they aren't more than one major release version apart. For example, any 1.X client will work with a 1.Y server. However, if the client and server versions don't match, certain features may not be available.

See the client/server interoperability policy is documented in the "Compatibility" section of the Subversion Commuity Guide.

But, you cannot use different Subversion clients with the same working copy, because Subversion working copy format is not backward compatible and Subversion automatically upgrade it to the latest format.