How many portable MP3 players were sold during the first half of 2004
in 1) US and 2) Europe

HI, i feel i may only be able to solve half your problem ($5). 
5.2million MP3 players have been sold in the first half of 2004.
The apple IPOD has accounted for 1.55million in the first half of the year. 

(results from NPD research centres)

by 2007, it is estimated that  the sales of MP3 players would of
increased to around 50million world wide.

Unfortunately i do not have statistics about the europe sales.

Paul

Paul,

Apple's results show 807K +876K = 1.683M iPods in their Q2 and Q3 = 1H 2004