ACTION: This step is very easy: you only need to download and install the VAC software. Once it is successfully installed, there is no need to even open VAC or configure VAC -- VAC runs silently in the background, automatically creating a music stream called "Line 1 - Virtual Audio Cable". We will use this Line 1 in an upcoming step.
Trial version of VAC available here.
Full version of VAC available here ($30 USD)
Other versions of VAC are available at various download sites around the Web.
VAC is 'routing' software for audio. This means: VAC lets you transfer music and voice signals from different software packages and microphones to play in other software or speakers/headphones of your choosing. This obscure-but-useful tool is the key to streaming music while also maintaining full voice communications in ventrilo.
VAC is a product authored by Eugene Muzychenko, a gifted programmer.
More details on this VAC requirement are available here.