Here are some links to very helpful webistes that will help you learn your parts for Vivaldi's Gloria. Follow the links, then choose the appropriate voice part and take a listen!
http://s119247422.websitehome.co.uk/midimusic/Vivaldi/Gloria/gloria.html - midi files with emphasized voice parts
http://www.cyberbass.com/Major_Works/Vivaldi_A/vivaldi_gloria.htm - midi files with emphasized voice parts
http://www.sad60.k12.me.us/~lowell/NobleChorusPage/VivaldiProject.html - mp3 files with actual people singing emphasized voice parts. Very cool, but not the best model of how we want to sound. Nevertheless, this can still be a very helpful site.
To download tracks, right click each link and click 'save as'. You will then be able to make a CD or put them on your iPod.
If you have found other sites with similar options, please email the links and I will post them here.