global-set-key with altGr on PC

[Sébastien Kirche]

Hi all,

to resolve the insertion of the euro symbol i have defined the 
following in my .emacs :
,----
| (defun insert-euro () "Insert Euro sign"
|   (interactive)
|   (insert (make-char 'latin-iso8859-15 164))
| )
| (defun insert-euro-unicode () "Insert Unicode Euro"
|   (interactive)
|   (insert (make-char 'mule-unicode-0100-24ff 116 76))
| )
`----

To help for easy typing, i have added that (for PC):
,----
|(global-set-key [128] 'insert-euro); C-h l gives \200 for euro 
(AltGr-e) = 128 dec
`----
This works fine.
But then i tried to add another key like C-u AltGr-e for 
insert-euro-unicode,
,----
| (global-set-key (concat "\C-u" [128]) 'insert-euro)
| or
| (global-set-key "\C-u\200 'insert-euro) ; \200 is C-q AltGr-e
`----
but it fails with the following:
error: Key sequence C-u C-M-@ uses invalid prefix characters

How can I define a global-set-key with C-u Altgr-e ?

Thanks for help.
Sébastien Kirche