I'm struggling to find out what size of SD card a Columbus sat nav can take for music playback.

I think I have read somewhere its only 2gb which seems very low. My current Bolero is much higher than that and all my music is on 4gb cards.

The car will be a Sept 2009 Superb and an excerpt from the manual says,

'Memory card case: SD memory cards (“Secure Digital Memory

Cards”) and MMC-memory cards (“Multimedia Cards”) measuring 32

mm x 24 mm x 2.1 mm and with a capacity of up to 2 GB are available.'

At the time it was written,2008, were only 2gb cards on the market

32GB, depending what firmware your unit is running.

So the card capacity is firmware dependent

The garage I'm getting the car from is putting firmware update 2664 or 2764 on and updating the maps using disc V.7

Will this be enough to get me up to using a 4gb SD card

Yes