Stop Clamwin in system tray

Get rid of the system tray icon that appears when you install a new version of Clamwin by opening HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run in regedit, and deleting the key with clamtray.exe in it.

Or use the excellent Clamwin Portable.

AC3 to WAV

To convert an AC3 file to WAV I used BeSweet's AC3 to WAV option. (The BeSweet GUI is the simplest way to do this if you aren't used to the program - though the file selection controls are a bit retro).

Extracting audio from VOB/IFO combinations

The method that worked for me was to use PGCDemux, pointing it to the IFO file and ticking 'Demux all audio streams' (and no other boxes). This produced an AC3 file which Media Player Classic was able to play.

Perl regexp grouping

A group which has ? after it to make it optional will 'use up' a grouping variable whether or not it gets matched. So

/(a)?(b)/

will place "b" in $2 whether matched against "ab" or "b".