A few points:
It might have helped if you'd have told us where abouts in Switzerland you're travelling to!
I frequently pay for things online and I always enter my debit card details where it says 'credit card' and I've never had a problem.
Young people seem to forgotten an invention called the telephone! It's often quicker and easier to get information (or make bookings) by picking up the phone than it is by going online.
If you're going to Geneva, it's too late to book the youth hostel online but you can still phone them. Details are here:
http://www.yh-geneva.ch/index.html
For other Swiss youth hostels, see here:
http://www.youthhostel.ch/home.html?&L=1
(Once again, a phone call might be the best way of making contact). You don't need to be a member to use these hostels but you'll pay slightly more if you're not. The charges, for non-members are about �15 per night are