well, I have also met the problem. But I am using kubuntu-artwork- usplash. I found the most simple way to solve it is modify /etc/usplash.com and change 640*480 into 1024*768.
-- usplash: no usable theme found for 640x480 https://launchpad.net/bugs/60621 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
