Hi, I am in Chennai and I also switched to Xandros only recently.
Configuration in Xandros seems easiest.
Basically, Sify uses HTTP based authentication. Also, they provide a client to use in Linux also. You may ask your provider or go to the IP for downloading the clients. Where do you live in India? I live in Chennai and can download the linux client from
http://202.144.65.70:8090/
There will be a link ("GNU/Linux users click here to download the Sify Broadband client"). You can download it from there.
If you need any help, just ask me.
Krupa