This year (2010) during Google Summer of Code a project for creating a Just-In-Time compiler for the Tcl language started its coding phase. It is still on a very initial phase, but it may be at least interesting to some people to get to know more about it without deciphering its code. The text below (after editing this for some more time) reflects the current state of the compiler.
Advanced Compiler Design Implementation - Steven S. Muchnick. This book starts right away indirectly mentioning the importance of different levels of intermediate representation. Converting the stack machine nature of the Tcl VM to quadruples was motivated by some of the reasons present on this book. (XXX There is also a JVM that does this, finding... XXX)