After my failure to get iPlayer content working on my 360 (as detailed in my last post), I tried another route, as suggested by IainB in the comments.
I had already activated Media Sharing in the Vista network control panel, so I simply turned both machines on and went to the Media blade, selected video, then pressed X to change source and selected my PC, which appeared on the list straight away. Then all the video content shared on my PC appeared in a list.
However, the 360 still wasn't able to play the iPlayer video content. After hitting play, the screen faded blank for a second, and then a blade appeared with saying it couldn't play the content with a hex error number (which I forget at the moment). It was able to view some images from my PC, though the connection kept dropping, which is odd, because the wireless network has previously been totally solid - copying data between our two PCs works flawlessly. I haven't tried playing music over the network yet.
I also discovered that you can plug a digital camera into the 360 via a USB cable, and it can display a slideshow of the images on the camera straight away. A really nice feature!!!
Looking at various websites it seems Vista has more problems with sharing this stuff than XP. People claim to have gotten it working, but have had to jump through bizarre hoops to get it to play.
I tried again today with the 2nd episode of the apprentice, but failed miserably to get it working.