The revelent peeps are probably already aware of this, but just in case, pictures released by NASA are copyright free (in the public domain).
http://heritage.stsci.edu/ = hubble heritage. Most of the decent picies are here.
You can probably use them for backgrounds and such like.
I personally would download them all and use them all for desktops, but 56k modem just can't take it
The actual Copyright notice:
"Material credited to STScI on this site was created, authored, and/or prepared for NASA under Contract NAS5-26555. Unless otherwise specifically stated, no claim to copyright is being asserted by STScI and it may be freely used as in the public domain in accordance with NASA's contract. However, it is requested that in any subsequent use of this work NASA and STScI be given appropriate acknowledgement. STScI further requests voluntary reporting of all use, derivative creation, and other alteration of this work. Such reporting should be sent to [email protected]."
from http://www.stsci.edu/institute/Copyright
And this post is almost certainly going to be my only contribution to the artistic side of this project