A statistics course
committed to honest data analysis,
focused on mastery of best-practice models,
and obsessed with the dynamics of financial markets
We will cover what we need to know about S-Plus in class, but if you want a further resource, you might take at look at Patrick Burn's A Guide for the Unwilling S User. Now there is no one among us who is in anyway unwilling, so the title is a bit off putting. Still, it does provide a quick no frills command line introduction to S.
A more complete tutorial --- one with all of the basis S knowledge that we'll need is the Dalhousie S Tutorial. This is still brief, but it does cover functions, loops and conditionals. It will be useful for you after you have a week or more experience, but if you dig into it immediately, you may just get yourself needlessly confused.
For the purely "Finmetrics" side of things, you can look to Zivot and Wang for more detailed information. In fact, the code examples that we do in class will cover almost all your needs. The only exception might be when you start to work on your final projects. By that time many of the students in the class will have turned themselves into S-Plus sophisticates.