okay, my WinXP really sends DHCP request into pptp tunnel - that’s good 
to setup dhcp server for pptp I even tried creating a bridge with DHCP server and setting ‘bridge’ in sercret’s profile - but pptp interface wasn’t added as a slave to that bridge…
by the way, the story is a bit ancient: http://forum.mikrotik.com/t/assigning-routes-to-pptp-client/8519/1
Normis, let’s start from the beginning?