I tried the Oxford CD-ROM and didn't find it particularly helpful. It's confusing because the basic module is ICAO and the UK RT is in a supplement which does not have the same degree of interactivity.
Really, RT is not rocket science. Get the free CAA document - it's up to date and has all you need. If you want to be interactive then find a friend or use a tape recorder.
There's also a FSX add-on which is supposed to be voice activated. I forget the name - but avoid at all costs!