I want to be able to add a press pack download to http://www.aliaskid.co.uk and I am wondering if it is a good idea to embed an MP3 of a song into a PDF file using indesign or whether this is even possible.
Yes, you can embed an MP3 file in an interactive PDF in InDesign.
Is it a good idea? That I can't answer. I am unfamiliar with what you mean by a "press pack download" and the website you're using.
The problem with including multimedia in a PDF is that there are many PDF readers, some incapable of properly playing multimedia. I'd suggest adding a recommendation that viewers of the PDF use Adobe Reader or Acrobat on Mac or Windows for multimedia. Most PDF readers on an iPad or Android tablet won't handle it correctly.
Great - that answers everything i need. Much appreciated