yes your cirrus card will work in most atm machines.
the problem with it is it will only allow you to take out 2000 baht a day where as the credit card will allow you to take out as much as you want
(well thats the problem i had) maybe as you say call the bank beforehand and let them know your going abroad.
Its best to get your credit card pin sorted.. good to have at least 2 cards when there incase you loose one. Most atms charge 150 baht for each atm transaction which adds up if you can only take out 2000 baht a time.
try the yellow ones outside the 7/11's most of these i found dont charge.
About places to go
Chang mai is good for trekking and temples its also about half the price for everything there compared to the islands down south.
There is a place called pai just north of it that you can go to and do your treks from there.
Phuket is a dump - patong is anyways, too many aussies and hookers

sorry aussie friends haha
ko phi phi is nice but expensive (for backpackers). They have done the upmarket shuffle already so they are just interested in the package holiday
tourists instead of the backpackers
koh samui is all package holiday makers also but i found this side of thailand alot nicer than the other (thats phucket and phi phi).
koh phangan and koh tao are the main backpacker islands. ko phangan for the full moon parties koh tao for diving courses.
Even if you dont dive go to ko tao for the night life anyways i enjoyed it more than koh phangan. its smaller and easier to get to know everyone - if you like blond hair blue eyed scandanivian girls that is.
Watch out for the thai mafia and always pay your bill no matter how drunk you are- your always being watched.
Dont drink buckets on your own.
You are a walking atm machine.. have fun with it and dont get offended.
Dont throw cigarette butts on the ground or expect a fine. locals can tourists cant.
Dont do/buy any drugs - even off tourists - most likely its entrapment and your dealer will get 5000 baht for selling it to you and you will get a free stay at the bangkok hilton or a large fine.
Also if you havent noticed bangkok is nearly at civil war. The red shirts are protesting on the streets. They move the protests around every day in the city so that they cause as much trouble as they can. so they can be in china town one day and schumkivit road the next day. The day i arrived there the busses would not go to koh san road so they told me that they
would only drop me 20 minutes away and i had to make my own way through the protests on foot. if your going soon i would advise that you skip bangkok at the start of your trip and take a flight either down south to the islands or up north to chang mai. Maybe it will be over by the end of your trip and youll have a few days in bangkok to enjoy.