Kristof,
For future reference, if you have a new question we usually ask that you create a new thread. That being said, here are some answers to your questions.
1) You can use the DAQmx Create Channel VI to create a channel and wire the desired name into the "name to assign" terminal. You can cacade multiple DAQmx Create Channel VI's to create multiple named channels. An other way to do this is to use the Measurement and Automation Explorer (MAX) to create a virtual channel for each channel that you want to acquire. Then you can create a task that includes all of your virtual channels. Once you have this task you can generate LabVIEW code from this task. To do this please refer to the DAQ Getting Started guide which can be found here.
2) I'm not totally sure what you mean by changing an XY graph info a waveform. An XY graph is meant for taking an array of x points and an array of y points and mapping this on the screen. If you have something of a waveform data type you would probably be better off graphing this on a Waveform Chart or Graph as opposed to an XY graph.
3) I'm a little confused by this question as well. In what context would you need to convert a time expressed in a string format to a dbl format? What would it look like in dbl format? LabVIEW does have a type called "timestamp" which is usually used to denote a point in time. It's actually the number of seconds since 6pm 12/31/1903. There is a VI to convert from a number to a timestamp called "To Time Stamp" which will convert a number into a timestamp. You can also use the "Type Cast" VI to convert from a timestamp into a U64 integer.
Something you might want to look at if you're just getting started with DAQmx is the "Learn 10 Functions in NI-DAQmx and Solve 80% of Data Acquisition Applications" Developer Zone article. Here's a link to it...
I hope this helps,
Justin D.
Applications Engineer
National Instruments
