MacOSX & MS VPN (PPTP) & MTU decrease

[mk]

I use NT/sp6 for WinGate.
I use MS VPN, DHCP
I use WinGate5.0.4 for NAT
When I connect from my Mac I have to decrease the MTU from 1500 (default) to 1200-1300.
Is it possible to set somewhere in WinGate mtu setting I need?

By the way
WinGate doesn't automatically dial when I call Internet. At first it did it but now doesn't.