How can I fix this?

[Andrew Secrest]

I have been having these symptoms intermittently for well over a month:
a) When a file or folder is selected in the Finder, the filename begins  
flashing. Sometimes this is accompanied by a continuous alert sound,  
sometimes not.
b) Dialog boxes appear unexpectedly and disappear instantly, because  
the default button is clicked automatically.
c) Line returns get inserted randomly in documents, and terminal  
commands are entered before I finish typing them.
It was this last that clued me in that all these symptoms could be  
caused by the return key sticking, but it's not, at least not  
physically.  Hitting the return key on the keyboard SOMETIMES makes it  
stop, but never makes it start.

I know it's not caused by something in user-space, because
a) the error message says 'mach_kernel'  and
b) it occasionally appears in single-user-mode or when logged in as  
root.

I started using a new Apple Extended USB Keyboard shortly before this  
problem appeared, but I'm relatively certain it's not the hardware,  
because it has never happened when I'm booted into OS 9.2.

How can I fix this?

excerpt from /var/log/system.log:
May 13 03:14:45 Andrews-G4 mach_kernel:  
USBF:	32954.675	 
+AppleUSBOHCI[0x17d0000]::ReturnOneTransaction(0xeec7b40, 0xec2b820,  
e0004051)
May 13 03:14:56 Andrews-G4 mach_kernel:  
USBF:	32965.675	 
+AppleUSBOHCI[0x17d0000]::ReturnOneTransaction(0xeec71e0, 0xec2b820,  
e0004051)

etcetera... (small sample.)

output from USBProber is similar:
Timestamp Lvl  	Message
     5.329 [1]	+AppleUSBOHCI[0x17d0000]::ReturnOneTransaction(0xeec7180,  
0xec2b820, e0004051)
    17.329 [1]	+AppleUSBOHCI[0x17d0000]::ReturnOneTransaction(0xeec7b40,  
0xec2b820, e0004051)