Plastic Flyer,
In answer to your first question, I believe (for what that's worth) that it is vital that all pilots are taught mental DR. Surely this is navigation in its purest and simplest form, and should be amongst a pilot's skills for use when required (airborne diversion planning being just one example).
As for your second question, I'm sorry but I dont't really have the time to go into that here, however, estimating track and max. drift are always a good place to start. I'm sure, though, that the others on (in?) this forum will oblige.
Regards, GT.