There is only one way to capture rain (or so-called rain) in a shot like this. You need to use a shutter speed of 1/60 sec and nothing else. And also you need plenty of sun. Yes this is true, and you need the sun to be in front of you. A lot of these shots are done using a springler from the garden. SSo if you need to shoot the rain falling on something and have the drops showing some great blurry movement, 1/60 is the trick and always against the sun. Take a look at this image of mine:
I take my picture about a year ago. It was simply rainy day. For that image i set ISO = 800 for shutter speed 1/125s, and thats it.
The real problem for me is how cover camera from water because i havent MarkII or something...
Thank you, Alexander! BTW, I just reread a great page about shooting it the bad weather: Tips for Shooting in Bad Weather by Wendy Green (http://technology.sympatico.msn.ca/Tips+for+Shooting+in+Bad+Weather/ Photography/Tips/Articles/tipsforshootinginbadweather.htm?isfa=1/link). Very interesting. There are some tips, how to protect the camera too.