The software that comes with USB KVM switches usually is for loading switch-controlling software on xp systems, not to make the USB switch functional.
My biggest complaint with USB KVM switches is the redetect delay when you switch between systems. You may have to wait 5 sec before you have full keyboard/mouse control after switching.
The positive side of using a USB switch is that you can boot windows without having the USB KVM switch pointing to the win box and later get full mouse/keyboard control. If youíre using a PS2 mouse/keyboard combo and windows doesnít detect them during the boot (i.e., the KVM switch is pointing to a different system), it is likely that they will not work after the boot is complete.
No experience with a DVI KVM switch, so canít help you there, but I wouldnít expect any problems.
Havenít found a USB KVM switch that I can strongly recommend, probably because I prefer the PS2 versions. You usually get a little more for your $$$ with a PS2 switch.
Currently, my personal favorite PS2 switch is the IOGEAR GCS614A for 4 systems (I own 2 of these), which includes attached PS2 cables and stereo speaker connections. US$69.99 @ newegg: http://www.newegg.com/Product/Produc...82E16817107419
For a more conventional setup, I use the PS2 Linksys ProConnect series switches, which come without cables. You can daisy chain these switches together and form a switch array. LinkSys ProConnect 4 system SVIEW04 (I own 2 of these) US$101.99 @ newegg, but currently has a US$50.00 rebate (US$51.99 after rebate): http://www.newegg.com/Product/Produc...82E16817107748
Warning: Good cables can cost as much as the switch.