Is this a computer speaking?

This site speaks for itself. Literally.

The prerecorded examples are amazing, just amazing. Around the edges of certain phrases, one still gets a bit of that flat, computery sound, but intonation and phrasing are astoundingly crisp, clear, and very human like.

The system also did pretty darn good with the various sample phrases I entered (e.g., it even handled, "If a weasel loving weevil loves a weevil loving weasel, then expect weevil weasel evil." with competence , if not grace; and yes, I made that up on the spur of the moment).

There are a lot of interesting TTS links on this site, including a cool comparison site---be forwarned, you can easily waste a lot of time there.

These folks are also doing work on lip synchronization on animated heads.

I'll note that Squeak also has some crude facilities for both TTS and talking heads. It's great fun to play with.