Hello and welcome to SL.
Whilst you shouldn't be seeing that error with Version 5.0, please note that in any case Version 5.0 is obsolete; the latest version released on LiveDVD is 5.4 (please see the Press Releases
section of these forums, and particularly the post announcing the release of the two main LiveDVDs Sabayon Linux 5.4 GNOME and KDE: Stable release
as well as the explanatory post amd64, x86_64, x86, K, G, Core etc. - What do they all mean?
I recommend that you download an ISO for the latest stable release (5.4), burn a LiveDVD and then install it to dual boot with Vista using the best procedure, which is given in the SL Wiki article HOWTO: Dual boot Sabayon Linux and Windows
Note that SL 5.2 and later use Grub2. Versions of SL earlier than 5.2 used Grub Legacy.
Once you have got SL installed to your HDD, before doing anything else please follow the procedure in SL Wiki article Fresh Install - What to do?
Note that, unlike Ubuntu, SL is a rolling release
distribution, which means that, once it is installed to your HDD, you need never re-install again if you use the package manager's upgrade command as explained in the SL Wiki.