1) A "Combo" drive can burn CDs, and read DVDs, but NOT BURN DVDs.
To burn DVDs, you need what Apple calls a "Superdrive"
2) By Apple's defenition yes, but, there are reports that if you buy a Lucent Wavelan card of some sort, and then use some sort of driver that some people have programmed, you could use that, instead. I think the driver is somewhere on sourceforge.net
3) eh.... dunno. eBay?