"wan't to run Mandrake 10 > OS and not sure if drivers are available for the Speedtouch 330 USB modem provided by BT so i can get BB connection..."
They are, it's just a case of telling Mandrake you have a Speedtouch modem when you set up the Internet connection. It will tell you to copy the microcode over from your driver CD, but you can also get it here: click here
"is there a good availability of software to perform most tasks that you can do in Windows XP..?"
This is a huge question: it really depends on what tasks you're interested in. :) Mandrake / Mandriva comes with thousands of programs, so yes, if you can think of something you might want to do with a computer there's probably a program that will do it.