I think its very possible to make a psp keyboard. BUT you would need certain drivers or software for the keyboard that you use on the psp.
I have put together links together so it gives you an idea of how to make it possible.
This Is The Idea
Get A "USB Gender Changer A Female to A Female" Adapter Which You Can Get Here
http://www.usbgear.com/computer_cabl...=106&catid=106
Get A "USB 2.0, A-M to 5 Pin Mini Cable" Which You Can Get Here
http://www.casecooler.com/usb2amto5pin.html
Then Get A USB Keyboard
Which You Can Get Here
http://www.usbgear.com/USB-Keyboards.html
(Connect The USB Keyboard To The "USB Gender Changer A Female to A Female" Then Connect That To The "USB 2.0, A-M to 5 Pin Mini Cable" Then Connect The "USB 2.0, A-M to 5 Pin Mini Cable" To The PSP.)
Get A "USB A-F/Mini B 5Pin-M Gender Changer"
Which You Can Get Here
http://www.casecooler.com/usbab5pgech.html
Then Of Course A USB Keyboard
Which You Can Get Here
http://www.usbgear.com/USB-Keyboards.html
(Connect The USB Keyboard To The "USB A-F/Mini B 5Pin-M Gender Changer" Then Connect That To The PSP.)
(Sorry if this is to noobish. But i have done this with a usb keyboard and my psp and i know you'll need a driver or software for the keyboard that you use to work on the psp)