I followed the link Brian gave earlier, to the new Lego Dynamic Blocks and Mini-Blocks. When I scrolled down the page I saw something else that was not there yesterday ...
"The Legacy Block library adds support for RCX actions and sensors to the LEGO MINDSTORMS NXT Software. There is a new block for the RCX motor, lamp, touch sensor, light sensor, rotation sensor and temperature sensor.
NOTE: In order to connect the RCX sensors to the NXT, a converter cable is required. "
This has been eagerly anticipated by everyone with both the retail NXT kit, and an old Mindstorms RCX .
The Legacy Library is available as English, French, German, Japanese or Dutch downloads.
- Tony N
PS As previously mentioned on The NXT Step, the converter cables are sold by Lego's online shop: http://shop.lego.com/