-ONLY for the advanced user: look into default MTU registry values with relation to the router you use.

Definitely only for advanced users, though there is a programme that can change MTU settings for ADSL users without having to muck around in 'the guts' called Dr TCP which can be getted at this place. I would, as you said, recommend that either the user be familiar with this sort of thing or consult someone that does first.