Sucon,
It sounds like you are using the instrument driver for the TDS 5104 DPO. There is also a driver for the Keithley 2001 digital multimeter. You can find these LabVIEW drivers
here. I would look through the example VI's that are included in these drivers to see if there is any way you can trigger the instruments at the same time. In the TDS 5104 driver there is a triggering folder found in tkds5000>>Configure>>Trigger, there might be something useful in here.
Also, there is an example VI called "Basic Level Triggering of Waveforms" that you can find in the NI Example Finder. To launch this go to Help>>Find Examples, then go to the search tab and type in "Triggering", this example should be one of the first ones that shows up. If you look at the block diagram of this VI there is a "Basic Level Trigger Detection.vi". Here is the description for this vi:
Finds the first level-crossing location in a waveform. You can retrieve the trigger location as an index or as a time. The trigger conditions are specified in terms of threshold level, slope, and hysteresis. You can use this polymorphic VI to perform trigger detection on a waveform or an array of waveforms. The data type you wire to the signal in input determines the polymorphic instance to use.
Please repost if you have more questions.
JenK