Can i get a prepaid sim card for my mobile phone in austria and europe?

Yes, a prepaid SIM is no problem. You can get them from different Austrian providers.

But you have to check the following points:

1.)
In the USA (if you from there) the GSM frequencies are 850 and 1900MHz (as far as I know), but the European frequencies are 900 and 1800MHz. So your phone must be able to work in least one of the European frequencies (900MHz or 1800MHz) to get a connection.

2.)
In Europe the provider sells phones (as part of an contract) cheaper than the normal price but these phones are locked to the Sim cards of the provider. So you are not able to use a Sim card of an other provider in one of these locked phones.

i don't know

Yes, you can get a sim card from any reputable carrier in Europe. You pre pay it yourself and then "pay as you go"

I would get a sim from each country you are visiting. Its cheaper that way rather than using 1 sim for all the countries. So say you are in England, get one from Virgin Mobile, O2 or Orange. Then when you are in Spain, you can get one from Amena or Vodafone, etc.

yes, you can