File Associations

I've been trying (and failing) to associate during unattended XP install:

1) txt,rtf,nfo,cue,inf,log & sif with wordpad

2) wav & mp3 with WMP

The aim is to make it happen after WPI.

After searching the net, I thought something like this would do the trick for each file format. it clearly doesn't work.

ftype txtfile="%Systemdrive%\Program Files\Windows NT\Accessories\wordpad.exe" "%1"

ASSOC .txt=txtfile

So what am I doing wrong? And what should I be doing?

Thanks in advance.