RewriteRule to subdomain returns 404 or 500

I am getting a headache.

Not strictly Drupal but related to how the .htaccess file is constructed.

I have a nice shiny new drupal based website hoorah!

I have a rather naff old website with static html pages. boo!

I have placed the old website in a subdomain so that the old content can still be accessed.

So I have :

http://www.mynewdrupalsite.com
and
http://oldstuff.mynewdrupalsite.com

All I want to do is if somebody clicks a link relating to an old page - all of which are in one directory that it redirects to the relevant domain.

So

if {
http://www.mynewdrupalsite.com/article/*

RewriteRule = http://oldstuff.mynewdrupalsite.com/article/*
}

*wildcard anything after article/

Should be easy right!?
If I use redirect 301 - nice and simple. It will either return a loop because drupal adds ?q=article/ to the url string, or not acknowledge the action at all and just return a 401.

If I try this:

Rewrite ^http://www.mynewdrupalsite.com/article/$ http://oldstuff.mynewdrupalsite.com/article/

I get a 500 server crash.

help!