No matter which OS you use, for safety matters you should always close "extra" ports whenever you can. However, it is often difficult to find out which ports you really need and which ones you don't. Some people start with the "close everything until its needed" philosophy for strict security while others only close those ports which are most threatening - its up to you to decide your threat level versus the inconvenience level.
As far as Vista being safer than XP, it certainly is but mainly because they have addressed many of the flaws that have always been part of XP security. If you ask if Vista is safe, however, my answer would be no PC OS is safe as is proven time and again.