I would read the xampp docs, I haven't ever used it, but if you need to set up a mail server(postfix) go over to
http://www.howtoforge.com/ and under the linux menu, there are some good how tos, I believe postfix is one of them. They can be a pain to set up correctly, the first time or so, so read the instructions first once before you begin, then follow them exactly and you should be in good shape.