I have finally managed to connect Amiga (MiamiDX) to a winXP computer with nullmodem cable. PC is connected to LAN and to Internet (via LAN). In case you need this, DON'T USE MDMCISCO.INF. Use this instead:
http://bwinton.latte.ca/Palm/ppp.html(and in Miami dialer put this:
SEND BREAK
SEND "CLIENT"
WAIT "CLIENTSERVER")
BTW, I wish you all Marry Christmas and a Happy New Year
:-)