[plt-scheme] loading plai language in mzscheme

Hi,

I was wondering how to load the PLAI language in a mzscheme repl. I
have a found a thread in:

http://groups.google.com/group/plt-scheme/browse_thread/thread/fb15dd113cf9fecc

about someone that had the same problem. I am using PLT Scheme 4.2.1.

I have tried the following, but no luck. Any help would be really appreciated.

Sorry if this is a newbie question, but I'm searching through the
documentation also without luck.

Aleix

------------------------------------------------------------------------
$ mzscheme
Welcome to MzScheme v4.2.1 [3m], Copyright (c) 2004-2009 PLT Scheme Inc.
> (load "chapter-06-6.ss")         ####### This is a file that successfully works in DrScheme
> (interp)
reference to undefined identifier: interp

 === context ===
/usr/lib/plt/collects/scheme/private/misc.ss:74:7

>
------------------------------------------------------------------------
$ mzscheme
Welcome to MzScheme v4.2.1 [3m], Copyright (c) 2004-2009 PLT Scheme Inc.
> #reader(planet plai/plai:1:3/lang/reader)           ######### Then CTRL-D (otherwise it gets stuck)
> (define-type)
reference to undefined identifier: define-type

 === context ===
/usr/lib/plt/collects/scheme/private/misc.ss:74:7

>
------------------------------------------------------------------------
$ mzscheme -i -l plai
Welcome to MzScheme v4.2.1 [3m], Copyright (c) 2004-2009 PLT Scheme Inc.
lib: standard-module-name-resolver: collection not found: "plai" in
any of: (#<path:/home/aleix/.plt-scheme/4.2.1/collects>
#<path:/usr/lib/plt/collects>) in: (lib "plai")
>
------------------------------------------------------------------------
$ mzscheme
Welcome to MzScheme v4.2.1 [3m], Copyright (c) 2004-2009 PLT Scheme Inc.
> #lang plai
standard-module-name-resolver: collection not found: #<path:plai/lang>
in any of: (#<path:/home/aleix/.plt-scheme/4.2.1/collects>
#<path:/usr/lib/plt/collects>)

 === context ===
/usr/lib/plt/collects/scheme/private/misc.ss:74:7

>
------------------------------------------------------------------------