how to use the bash provided by macports

[Eckhard Wiemann]

Hi everyone,

does anybody know how I can tell my xterm to invoke the new bash 4  
(which I installed via Macports) when starting up? My wm is  
ratpoison, but ratpoison does nothing than to start xterm. Ratpoison  
in turn is invoked by X.app via ~/xinitrc.

===

MacBook-Wiemann /Users/eckhardwiemann:
which bash
/opt/local/bin/bash

===

MacBook-Wiemann /Users/eckhardwiemann:
echo $BASH_VERSION
2.05b.0(1)-release

===

MacBook-Wiemann /Users/eckhardwiemann:
echo $SHELL
/bin/bash

===

In my Aqua-Terminal I can use the opt/local/bin/bash, but when I work  
with cmd-lines I like to work with X11 instead of Aqua.

I think I have to reset an env variable like SHELL, but I can't  
figure out how to change it BEFORE bash ist invoked.

Any hints (also links on the Internet where I can learn more about  
these mechanisms) would be appreciated.

Thanks!

Eckhard.