I wish I was having as much luck!! I have been watching this very informative thread since buying my AE in December and, just as I was about to ask a question, the intermittent playing of iTunes seemed to resolve itself. Unfortunately it is back - and how!
HOWEVER - yesterday I had my Epiphany - and what a revelation THAT was! It has nothing to do with the AE.
My original wireless network is a generic 802.11g card in an XP Pro box and a D-Link 604T router/base station. This is upstairs in my office.
I wanted the Airport Express to connect to my hi-fi downstairs - to run specifically off my HP pavilion ZT3300 laptop. I set AE to join my existing D-link network and, whilst I had no problem getting the 2 to recognise each other, I have been plagued by these intermittent iTunes problems. I tried changing from a dynamic to a fixed address; I set robust connection. In fact I followed all your advice in this thread..
My AE was downstairs in a cupboard surrounded by steel dexion shelving (where my hi-fi is located), so I brought it out into the main room just in case it was being shielded. The problems remained.
I then moved my D-link downstairs so that the laptop, AE and D-link were only feet from each other - still intermittent problems. Sometimes iTunes plays for hours flawlessly, other times, it won't get through the opening bars of a song!
ANYHOW...
...as a test, and before I sent the AE packing, yesterday I installed iTunes and the relevant software on my XP box upstairs and iTunes now runs flawlessly. I have even moved the D-link back upstairs and the AE back into the cupboard. And it still plays. In fact I can't get it to go wrong now.
So it appears that it never HAS been an AE issue - but a laptop one. But what? Why?
When I hardwire the laptop into the hi-fi I have no interruptions, so it's not a defrag or drive spindle-speed issue?
Long post - I apologise - but any ideas? My drivers and firmware are up-to-date.
Thanks
Jonty