SQL 2005 License Key

Hi 

I'm just installing SBS 2003 R2, my second time around. I've got to the 
point that I want to upgrade the MSDE instance to SQL 2005 that comes on
the 
Premium Technologies Disc. When I ran the setup.exe I get prompted for a 
license key, so I went back and ran the top level setup which gives the 
option to install ISA 2004 or SQL 2005 from an application window. I click
on 
SQL 2005 and the same thing occurs, I get past the basic config and then
am 
prompted for a license key. I'm fairly sure this key should auto-populate
but 
it hasn't. The only thing I haven't done which I can think might be
affecting 
it is activate SBS online as I'm still running my first install of SBS on
old 
hardware. I've been avoiding activating it so that I don't have any down 
time. 

Can you suggest what it might be, and if it is simply that I haven't 
activated SBS yet? Otherwise, do you know where the key is stored?

Thanks

Adrian