Currently Being ModeratedJul 31, 2012 10:51 AM (in response to pgonzalez)
Provided you are in a region that permits redownload of previous purchases, go to iTunes store and select purchased from the quicks links.
You will see all previous purchases and you will be able to download the songs again.
Currently Being ModeratedJul 31, 2012 11:37 PM (in response to pgonzalez)
Jimz's advise is helpful. But to answer your question, no, iTunes Match will not automatically download anything. In fact the service is not designed to be a backup nor should it be used as such. See this thread for more information: FAQ: Why iTunes Match can NOT be used as a backup!
The best practice to restore your personal data to a new machine is to use a Time Machine backup (or backup created using some other trusted backup software) from an external HDD.