After that, it works just fine:
# cat /dev/usbtmc0 Minor Number Manufacturer Product Serial Number 001 Rigol Technologies DSA815 DSA8AXXXXXXXX
Here's a very simple and very bad python script which can be used to connect to a device, send commands and view the results (the output file stuff is device specific so don't use it): http://paste.kde.org/625808/
At this point, a big WTF towards the blogger editor: It's impossible to insert the left and right angle chars correctly if they are arranged like for C includes. If you paste them in the WYSIWYG mode, they get interpreted as HTML tag (!) and if you input them in HTML mode, they're displayed as... I can't even write it down, since the WYSIWYG mode obviously translates ampersand-sequences to characters... you know, those &; sequences. Come on, that can't be so difficult to get right.