Depends on the keyboard.
Most keyboards should allow different horizontally placed keys to be pressed simultaneously (ZXC for instance) but not vertically (WSX etc)
Although I was lucky enough to have one keyboard which allowed the same-time pressing of literally every key on the keyboard.
Also, a controller such as the DJ Dao won't have such problems at all.
If one is forced to use the keyboard, try a layout of ZXCVBNM as the keys. Same-time pressing of those keys should be possible.
Last edited by Ultra Violette : 02-11-2007 at 06:49 PM.
I found older USB and really old IBM Model M keyboards are usually able to handle 3 or more easily, I usually use an older Microsoft Internet Keyboard from like 1999 or a really old IBM keyboard I got with my Windows 95 computer.
If you were to get a controller, however just like tomokosasaki said, it wouldn't have this problem.