I skied up until last season when I decided to snowboard. For some reason I decided early on that I would try to learn on my own (being the smart cookie I am -_-) so I watched a whole bunch of Youtube videos online.
The first day went great and I went once every weekend for a month last year. On the fourth/last day I was able to go on the black diamonds. Keep in mind that I live in Illinois where black diamonds aren't steep.
My favorite videos:
The Snowprofessor series
How to Snowboard the Definitive Guide (it looks outdated but it's one video and it's very informative)
But if you have the money you should definitely get the private lessons if you only have two days.