I'm not sure if it is a Win7 problem, but since some days I get this strange ? signs after getting album/track-informations from Amazon with the amazon webscripts.
Please have a look at this example: 
This happens not only to spanish vowels, it's the same behaviour for german and french vowels as well.
That's because Amazon supplies bad data.
Are you sure, that this is not a codepage/encoding problem?
If you browse to amazon.com and search for 'Manolo Garcia' and 'Saldremos' I can't find such strange signs in the tracklist. There are 3 result pages for this album. All seems to supply the correct data.
On the other side, this appears not always with vowels... 
Yes. Mp3tag does not get the tags from the website but from the xml api.