Wrong. You set it up LAST tax year. FYI The tax year begins on the 6th of April each year, so the current year started 6th April 2011, and ends 5th April 2012.
So you opened it last year, and are eligable to open a new account anytime you like until 5th April, and then you can open one after 6th April as well (the following tax year)
Transferring cash from existing ISAs (like your Santander account) to a new ISA is possible, but not with every account type (you need to check with the new ISA provider that they allow transfers in). This will allow you to transfer the full amount + your yearly allowance (can't remember how much this is, think it's £5100). Obviously if you've been putting money in the Santander since 6th April 2011 that counts as this years yearly allowance.
Typically I tend to look for the best ISA deal come early March, and re-new my ISA to get the best deal in that month. The idea being that if there's a sudden change in the economy circumstances (bank of england increases interest rates for example....
lol...as if) but come 6th April you can transfer again to take advantage of the current improvement in circumstances.
Also it's often worth going into the bank to speak to an actual person, I was about to transfer my ISA away from LloydsTSB as my initial intraductory interest rate had ended (reluctantly as they're my main current account and card provider, and one login screen is very handy). Anyway right there she clicked some buttons and reset it to give me 2.5%, now that wasn't market leading but the 0.5% difference amounted to less than £100 given my low saving at the moment due to house extensions and wedding, and so it was more conveinient to stay with them, so that's always worth consideration - the hassle factor