Read also
http://java.sun.com/products/cldc/faqs.html In regard to your specific question, here's what is said:
"7.What is the target device for J2ME CLDC?
* Processor:16 bit/16 MHz or higher
* Memory:160-512 KB of total memory available for the
Java platform
* Power:Limited power, often battery powered operation
* Networking:Connectivity to some kind of network, usually with limited bandwidth "
In principle, the RI is portable to a 16-bit machine, it can only be used for free for research purposes. It comes customised to Linux, Sparc and Win32.