Does anyone kno what type of dvd media the following dvd burner burns?

HL-DT-ST DVDRAM GMA 4020B

Well it's obviously a DVD-RAM burner of some kind. Are you considering buying it? or did you just get it? I would need a brand on it before I could give you any more details (i.e. Matsushia(Panasonic), Toshiba). Unless you are sure that it burns some other kind of DVD media don't touch the drive (unless it's a freebee) as DVD-RAM media won't work on anything outside of your PC unless you have a standalone DVD-RAM recorder.

I believe the brand name is HL-DT-ST

Could be a Toshiba then in which case I wouldn't buy it as that particular drive is DVD-RAM only and will limit you to the options I listed above and the media is VERY EXPENSIVE. If I remember right to the tune of about $8-$10 a disc which translates into about 4-5 pounds a disc in the UK. Toshiba does make a DVD-R/-RW drive which is pretty good but that model you have listed isn't it.