[PHP] Append a line to a Text File

[Rodrigo]

I still need to know how to do it, since the "a+" or the "a" give me
problems...
I need to be able to add a line at the end of a text file thru sending
the information (and by this I mean the e-mail to be writen) thru a
form, and this new information should be added to the file at the end of
it without overwriting it.
Thanx,
Rodrigo
 
PS: If possible send a code for instruction. ;)