As long as you pay their minimum monthly repayment amount then yes you will be repaying interest free for 12 months. If you're looking to withdraw cash then that's usually exempt from the 0% interest offer so just use it for purchases.
Going with your own bank has the benefits of them probably using their internal file to gauge your credit worthiness so you'll likely get a higher a credit limit, plus less to fill out - just pop into your branch and speak with an advisor and they'll send out the card/information.
I got a 0% for 15 months card last June-ish, I'm 23 and it was my first card. Bought myself the parts for a new gaming PC and a 60" Samsung Plasma in the first week.
I'm close to paying it all off now having paid no additional interest. I think if you're sensible enough and you realise you'll have an additional £100+ of outgoings every month for the next year then you'll be okay. If I didn't have relatively good job security I wouldn't have done it though.
What bank are you with out of interest?