I disabled the Compiz Fusion on Ubuntu 7.10 host, the problem gone on the Ubuntu 7.10 guest.
My friend's Lenovo ThinkPad T61 (Intel Core 2 Duo T7250, nVidia Quadro NVS 140M display card) running Ubuntu 7.10 host with Compiz Fusion enabled and Windows XP SP2 guest but no such problem.
UPDATED : I also checked with other distibutions as guest with Compiz Fusion enabled, such as OpenSuSE and CentOS, in the same manner. I think it is not the problem of the the guest OS.
I am running 32-bit host and guest OSes.