The problem with trying to buy a vehicle is getting it insured. You probably can't get it registered to your name since you are not resident in any of the countries you wish to buy a bike from. Without being able to register the bike you can't insure it, or tax it. No insurance or tax means you are illegal which would lead to major problems.

You also need to check out whether you need a Schengen visa (and any visas for non Schengen countries on your list) and want the conditions are attached to that visa - you may have to give a list of places you intend to visit and where you intend to sleep, plus exact dates, which would put a damper on freewheeling around Europe. To find that out you need to look at the embassy sites for the countries you want to visit or their tourist information sites for India.

As others have said though you should visit the Thorntree forum for more chance of help.

I know zilch about your inquiry but can use Google pretty well:

http://www.rental-motorcycle.com/europe/europe_rental.html

Guided tours:
http://www.smtours.com/
http://www.bosenberg.com/

Thank you hetismij. I was worried about that only. Thanks for clearing it out. I guess i'll have to modify my plans or get some relative or friend in europe to buy a bike for me.

And thanks travelnut, these websites are really useful.