Rather than having "vitae" mean "lives," another way to look at the usage of "curriculum vitae", is that if you want it to mean "path of [one's] life" (a somewhat literal translation of the term), you have to decline the noun "vita" and use the genitive case (typically indicating possession), which is  "vitae".  
 
Julia Moore
(yes, I was a Latin major in college and this is one of the few chances I get to use it, aside from annoying friends with pedantry)
Speaking of which: 'Vita' means 'life' whereas 'vitae' means 'lives' . . . it just makes sense that this rule of singular vs. plural applies to the term under consideration.  'Curriculum vita' is singular and 'curriculum vitae' is plural.  So, while I have a 'curriculum vita', most human resource specialists in museums are buried under several mounds of 'curriculum vitae' for each job opening.  <smirk>
 

Jay Heuman, Visitor & Volunteer Services Coordinator
Joslyn Art Museum, 2200 Dodge Street, Omaha, NE, 68102
342-3300 (telephone)     342-2376 (fax)      www.joslyn.org