Once upon a time I wrote a review for the Logitech Media keyboard. Well since then I have changed my Quake 3 movement controls from wasd to esdf to rdfg to increase the number of available keys for weapons and team binds. Anyway, once I switched to rsdf the keyboard would be incapable of accepting more than two keypresses. Two? Thats fucking miserable, I thought. The limited number of keypresses which the keyboard would accept would prevent me from being able to perform a proper bunny hop and a weaponswitch at the same time which, although you might not realise it, is something which happens quite often whilst playing. Anyway, I figured I might need to get a new keyboard, I believed the problem was with limited bandwidth from the PS/2 port. Yesterday, however, I fixed the problem.

Keyboard keys are arranged in areas called matrices. Each keypress transfers a signal to a given wire present in the matrix. It is best when gaming to use all of the keys present in one matrix so that there are no conflicting keypresses which send two different signals down the same wire. Wtf? About 2-4 wires are hooked up to each keyboard matrix. If you press a key which sends a signal down a wire attached to that key in the key matrix, and then press another key in a different key matrix which is attached to that same wire, you're asking that single wire to transfer two signals at exactly the same time. On most keyboards, the damn thing is made to transfer only one signal, albeit very rapidly. When you press multiple keys which end up sending signals down the same wire, the computer or keyboard can't process the second keybress and gives you that oh-so-fucking-annoying BEEP.

Yesterday I found a program which displays which keys the computer receives as they are being pressed. Now I tested my rsdf combination. I pressed r and d at the same time. Both of them showed. Then I added t and space bar separately. Guess what? Neither of them showed. The two keys I was already pressing were from different key matrices so I suppose it was the most the keyboard could take. Accepting the bad news, I tried different combinations until I finally came accross one which works beautifully and accepts up to four simultaneous keypresses (of course it also depends on which keys, because their location is directly related to their key matrix). What combination? IJKL :D I'd say IJKL or WSAD is the best for Logitech keyboards because of their key matrix layout.
The program is called KeyScan v0.9, programmed by a group/individual called Digital Genesis. I recommend it to anyone who has similar issues as I did with the keyboard refusing to accept a certain number of keypresses.
You can download the 35kB program here or download it from the ESR server (I uploaded it).
*UPDATED BIT* I found something in the control panel/accessibility options menu which may fuck things up for some users. FILTERKEYS. This particular bitch can make your keyboard ignore repeated keystrokes. You can try to configure it though - it has some interesting options
1) Click FilterKeys settings
2) Check "Ignore quick keystrokes and slow down the repeat rate"
3) Check "Slow down keyboard repeat rates"
4) THEN decrease all values to their minimums - repeat rates and delays of pressed keys will be even lower than what you can configure in the control panel. I don't know if this helps multiple keypresses but it sure will get the problem of repeated keypresses out of the way. I haven't tried this yet in Q3 (no time - I party too much), would be cool if someone could try this.
I'd recommend disabling the other keyboard shortcuts (StickyKeys, ToggleKeys) they're plain useless.
GL!