the motherboard specification stated that my motherboard has 8xUSB 2.0(rear X4/froun X4) ports, but all my usb devices connected can only perform at USB1.1 speed.

I am using kubuntu 6.10, from the KInfoCenter I can see both EHCI Host Controller(USB2.0) and UHCI Host Controller(USB1.1), but all my devices are connected to the 1.1 controller.

anyone can help?

Not for certain but I can make one suggestion for you to investigate:
Do you know if USB 2.0 support is enabled for your kernel, either compiled in or as a module? You **may** need to explicitly compile it or make the module, and then insert it.
If you browse through /lib/modules/<your-kernel>/ you might see something called USB_EHCI_HCD.ko (and then again you may not, if it has to be compiled in, instead of as a module). If you see this, try 'modprobe usb_ehci_hcd' in a root console.
If you DON'T see it, I would *guess* the support isn't enabled in your kernel, and maybe look into running xconfig and rebuilding your kernel with the needed support.