[R] attach and detach question

[markleeds at verizon.net]

I have a large R program that I am constantly running over and over again. At the beginning of this program, I create a hige matrix and a huge dataframe but these are constant. What I mean by constant is that, if I run the program over later, I really should just use the old matrix and dataframe ( if they exist ) that were created in a previous run so that the program doesn't have to spend time creating them. Unfortunately, I don't know how to do this so things take foreeer because every time i do a new run, i recreate these objects and the boss is getting a little annoyed. I know/think that I should use attach and detach commands  but 

1) i can't find an example somewhere of
just saving two objects rather than the whole session.
i've looked and looked and i can't find it.

2) if i am able to save these two objects, i was hoping that it
would be possible to write code inside my R program
that basically says, "if these objects already exist in
such and such database, then skip over this section of the code
that creates them".

if someone has some code or a page number or reference, this is fine because i used to do pretty much this in Splus so think i can figure it out if i can just find an example.  thanks a lot.