If the Mac mini now comes with a UJ-835 model Superdrive then it can write to DVD-R at 8x (unless Apple crippled it).
Check it out here:
http://www.dfwdepot.com/osc/product_info.php?products_id=139
Check it out here:
http://www.dfwdepot.com/osc/product_info.php?products_id=139