Connie,
Talgos are fast trains but not high speed trains. Take for example Talgo trains from Madrid to Barcelona. They take more or less the same as buses so if a train runs only as fast as a bus, I wouldn't consider it as a high speed train.
As you said, high speed trains by definition are only AVEs (in Spain), TGVs in France... I'm not sure but I think Talgo trains run at a maximum speed of 120 Kph, whereas AVE runs between 300 - 350 Kph.
Just think that Talgos from Madrid to Barcelona take about 7 hours, AVE to Barcelona will take only 2 hours 20 minutes and planes take 1 hour. Do you see why we don't refer to Talgos as high speed trains?.
About flights, you're right. Only roundtrips have good offers. You won't probably find a cheap ticket for one way.
Regards,
Antonio
------------------
The best tips from your favourite hostal in Madrid.
Hostal Chelo at
http://www.chelo.com