From the web site where you can download the SP...
"Windows Vista SP1 RC Refresh is time-limited software.
Windows Vista SP1 RC Refresh will no longer operate after June 30, 2008
and should be uninstalled prior to that date. After installation your
desktop will show the text "Evaluation Copy". This does not mean that your
system is no longer genuine but that you have installed a test version of
software which is time-limited. The "Evaluation Copy" text will appear on
your desktop after the second reboot after installing the service pack.
Likewise, the "Evaluation Copy" text will remain on your desktop during
the first reboot after uninstall the service pack, but will disappear
after the next reboot.
"