Dont pay for any info from ebay mate, there's one guy that sells info thats in the handbook... Google and forums are the way forward. Pull the CD30 and look at the wiring diagram to see if it supports aux in first. There seams to be several different versions of the CD30, some aux enabled, some MP3 some powered normally and some like in the Vec C and Astra H that are Can-bus.
There's a link here to VXRO with some info, its for an Astra H but the info is good.
http://www.vxronline.co.uk/forum/showthread.php?147284-cd30-aux