Only the ones for services you are providing. You will need to open the web port if you are providing web services, and the FTP port for providing FTP services.
If you aren't running any services, you don't have to open any ports.
I thought all ports below 255 can't be firewall protected. I might be wrong, but those ports are reserved for standard services, right? (such as http, https, smtp, pop, imap...)
