Whereis the pltcl.so file for postgres7.2.3??

I don't have tcl in my database. And I have done it as su - postgres and
only then createlang pltclu ion. But Now I'm getting the error that says,
	pltcl_call_handler does not exist

Is it because I have downloaded pltcl.so file and tried installing it afetr
I have already installed postgres? Is it a MUSt that I install tcl along
with postgres? Or is anything else wrong?

Thanx
MAdhavi