Are you using Google Chrome already? Then do check the hack to run userscripts on Google Chrome. Well, this hack will allow you to run multiple instances of orkut profiles in Google chrome.
How to Run Multiple Orkut Profiles in Google Chrome?
- Install Google Chrome Backup
- Run this program and it will offer you an option to create a new google chrome profile.
- Create as many profiles and open each using this program.
- You can login to different profiles in each window.
- Similar hack is availiable for firefox.
Gaurav Dua – Orkut Guru – 539 Points 
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[...] I am not sure if many would remember but we have once shared the trick to sort out Greasemonkey Crashing issues. In case you do, then yes, the same tutorial will be enough to allow you set up multiple Firefox profiles thus will allow you to run multiple instances of orkut profiles (a similar hack is also available for Google Chrome Users). [...]