The same issue with Leopard 10.5.8 running the last supported (vintage) iTunes player with internet radio, here; in that the hardware does not matter, and since early March (this year) the Radio no longer loads stations and so there is nothing to stream from the different lists of music types.
So, my first-edition MacBook1.1 13" 1.83GHz coreduo has the same problem as my mid-2005 iBookG4 12" 1.33GHz, and Late 2005 Mini G4 1.5GHz; all run Leopard OS X 10.5.8. The Intel-based MacBook1.1 has a means of using later iTunes Radio (or try to) with Snow Leopard upgrade afforded the hardware design.
Other users had suggested to look online to get the URLs of radio stations who offer streaming audio for free and get that web address, manually enter it into the iTunes player (in specified place, so it looks for it online) to return to some limited use of the iTunes internet Radio. And I had read of a few workarounds to attempt to connect to a server that may/may not support a stream. Or at least look into a server where one could get URLs to manually load one at a time into iTunes Radio player. Not sure how or if it would save them, and have not tried this.
In a few locations across the globe, vintage iTunes radio will
still sort of work. Guess it depends on the server support.
Mine have iTunes 10.6.3 in Leopard 10.5.8.
When I had unlimited ADSL internet, w/ no broadcast radio music
the ability to leave internet stream on something all the time was
a great deal, in that I used iTunes Radio to test the ISP most the
time and was an unpaid beta tester at high retail cost, since I
could spot issues before their system failed. They were unwilling
to accept troubleshooting suggestions to prove my point, until
after they had major server failures and long outages. Now I am
stuck with a poor overpriced cable provider with a bundled kit.
Good luck with any attempts to restore partial use of iTunes Radio. 🙂