I have a PS2KVM4 and I'm using a PS/2 keyboard, which works great. Even the USB keyboard works great when I use a USB to PS/2 adapter. However, I have a USB optical mouse (pretty standard, just two buttons and the wheel) and when using the PS/2 adapter I don't use of my mouse. The optical light is there, but there's just no use of the mouse on any of the three computers that I've got it hooked up to; which are WinXP SP3 x86, Fedora 7 x86, and a SmoothWall firewall.
The cheap Belkin 2-port PS/2 KVM worked fine with the USB to PS/2 adapter, but the Linksys seems to have a problem.
Check your F2...Set-Up Program...and if your PS/2 selection has a CHANGE---for...AT...that may work...for your USB-type Keyboard and Mouse...I prefer PS/2...the USB...Keyboard and Mouse that came with my DELL Purchase were small ITEMS...I switched over to PS/2 for a larger keyboard...BUT...F2...System Set-Up Program should have something for an AT-computer....<<---which is a USB-type Keyboard and Mouse.