@Rhys > In the first instance you mention, are you connecting wireless from your laptop to the Aero or through another wireless device or are you talking about playing from a USB stick? Have you any firewalls / antivirus enabled?
Where do you get your MP3 files from? Do you edit them / encode them after purchase?
In relation to your USB sticks, what make / brand are they? Have you formatted them to FAT32? If so, which utility did you use to format them?