When I installed the solution, I also got prompted for username and password. However, when I input de domain adminsitrator account and pass, the installation completed succesfully..
Anyway, I've found before in other installations of sharepoint, that sometimes even when I login as the domain administrator, i get rejected. I've always fixed this by disabling kerberos in the IIS application. In this case the SharePoint Central administration
app. You could try that and if is doesn't work, just enable it again if you want.
Here is a page that explains the procedure from SharePoint: http://support.microsoft.com/?scid=kb;en-us;871155&x=7&y=13
HowEver, I've always done it manually, buy finding the App ID in IIS, and the from command prompt running
cscript adsutil.vbs set w3svc / <var>WebSite</var> raíz/NTAuthenticationProviders "NTLM" as explained in this site: http://support.microsoft.com/?scid=kb;en-us;215383&x=8&y=9
but instead of "Negotiate, NTLM" I just put "NTLM"