How to configure TMG 2010 (server) + Cisco 871 (client) over PPTP VPN?

Question

Computer networks

Good day,
there is TMG 2010 and several Cisco 871 with IOS 12.4.
I want to set up a VPN between them via PPTP, since Cisco 871s are weak and I don’t want to load them with encryption, I want to squeeze the maximum speed.
I tried a couple of options, there is very little information on the Internet about using Cisco as a PPTP client, and even more so in conjunction with TMG2010.