how to save strings to a temporary buffer?

[ed_tsang at yahoo.com]

How can I save string to a tempororay buffer and then write it to a 
file afterwards?

I have a function that output a formatted string each time it is 
called; but instead of open a file and write it each time; I would 
like to save these strings to a , may be a tmeporory buffer, and then 
write it to a file when everythign is completed... how cna I do that?
thansk