[plt-scheme] scribble ultra beginner

Hi,

I'm *really* just starting to try to use Scribble. 

my very elaborate test is as follows:
---
#lang scribble/base

@title{Hello world}

This is hello world
---

Now, if I click on HTML, it works (browser opens with the formatted page) but I get a warning:
 [Output to /Users/etanter/Develop/Scheme/Scribble/test.html]
2010-04-27 13:46:15.034 osascript[31959:903] Error loading /Library/ScriptingAdditions/Adobe Unit Types.osax/Contents/MacOS/Adobe Unit Types:  dlopen(/Library/ScriptingAdditions/Adobe Unit Types.osax/Contents/MacOS/Adobe Unit Types, 262): no suitable image found.  Did find:
	/Library/ScriptingAdditions/Adobe Unit Types.osax/Contents/MacOS/Adobe Unit Types: no matching architecture in universal wrapper
osascript: OpenScripting.framework - scripting addition "/Library/ScriptingAdditions/Adobe Unit Types.osax" declares no loadable handlers.

any idea?

If I click on PDF, I get no result, just an error:
run-pdflatex: could not find a `pdflatex' executable

 === context ===
/Applications/_Extra/Devel/PLT Scheme v4.2.5/collects/scribble/private/run-pdflatex.ss:7:0: core
/Applications/_Extra/Devel/PLT Scheme v4.2.5/collects/scribble/private/indirect-renderer.ss:38:8: for-loop
/Applications/_Extra/Devel/PLT Scheme v4.2.5/collects/scribble/run.ss:90:0: build-docs
/Applications/_Extra/Devel/PLT Scheme v4.2.5/collects/scribble/run.ss: [running body]
/Applications/_Extra/Devel/PLT Scheme v4.2.5/collects/scribble/tools/drscheme-buttons.ss:24:3
/Applications/_Extra/Devel/PLT Scheme v4.2.5/collects/scheme/private/more-scheme.ss:158:2: call-with-break-parameterization
/Applications/_Extra/Devel/PLT Scheme v4.2.5/collects/scheme/private/more-scheme.ss:274:2: call-with-exception-handler

I understand this is a path problem, because I do have pdflatex:
$ which pdflatex
/usr/texbin/pdflatex

How can I configure scribble so that it finds pdflatex?
(I'm on mac os 10.6 with drscheme 4.2.5)

Thanks!

-- Éric