See this recent thread:
http://discussions.apple.com/thread.jspa?threadID=2722609&tstart=0
If you decide to go with an eMac, the 1.42G is the only way to go. Reasons are in that thread.
The 1.42G eMac shipped with a minimum of a Combo Drive (reads/writes CDs; Reads DVDs). If you must burn DVDs, get one with a SuperDrive.
The biggest problem with buying an eMac from eBay or, really, any non-local source, is the high cost of shipping as 50-pound (23kb) object. That can account for a significant percent of the purchase price.
If you are keen of watching online video or streaming video, no G4 will do it well any more. Even some G5 Mac owners are reporting trouble. Modern web video is optimized for Intel processors. Like others here, I suggest an Intel Mac. My daughter has an entry-level Intel Mac Mini that runs circles around our most-capable G4 Macs. And a Mini weighs only about three pounds--cheap shipping.