I have the same problem here (Host: Windows XP, Guest, Ubuntu 10.04 beta, updated to latest as of 4/2/10). The keyboard doesn't work at all at the login screen, but the mouse works fine. I can access the on-screen keyboard to log in. If I log into KDE, the keyboard still doesn't work at all. However, if I log into Gnome, the keyboard then works fine.
I have the same problem here (Host: Windows XP, Guest, Ubuntu 10.04 beta, updated to latest as of 4/2/10). The keyboard doesn't work at all at the login screen, but the mouse works fine. I can access the on-screen keyboard to log in. If I log into KDE, the keyboard still doesn't work at all. However, if I log into Gnome, the keyboard then works fine.