Two issues I've had regarding the last XP compatible version of Steam are invalid SSL certificates for the CEF and in-home streaming not working on my client machine when running XP x64 (works fine under 7 x64).
The latter is especially troublesome.
At first, streaming_client.exe couldn't create a socket. I fixed that by installing the IPv6 protocol on the XP client. Sadly, the streaming client still fails with the "Couldn't connect to the remote computer." error.
Updating root certs and using ProxHTTPSProxy didn't fix anything.
Any advice?