Two keyboards will work. As mentioned, you can use a PS/2 splitter, or use a combination of a USB and PS/2 keyboard. For what it's worth, you can have up to 127 USB keyboards.
Player: Pentium 166MMX, Amptron 598LMR MB w/onboard Sound, Video, LAN, 10.2 Gig Fujitsu Laptop HD, Arise 865 DC-DC Converter, Lexan Case, Custom Software w/Voice Interface, MS Access Based Playlists Car: 1986 Mazda RX-7 Turbo (highly modded), 1978 RX-7 Beater (Dead, parting out), 2001 Honda Insight
"If one more body-kitted, cut-spring-lowered, farty-exhausted Civic revs on me at an intersection, I swear I'm going to get out of my car and cram their ridiculous double-decker aluminium wing firmly up their rump."