The Keyboard
I'll start with the keyboard, as it was the easiest (relatively!) to procure. You could, theoretically, use any computer keyboard that you want, be it old, new, membrane-style or otherwise. In fact, some people have "done a Steampunk" on a standard, modern Dell keyboard. However, both Jake and Datamancer (who I consider to be the leaders in the field) recommend using an IBM Model M keyboard.
The reasons for this are as follows (and I have to say that I totally agree):
The keyboard - manufactured between 1984 and around 1990 - is the most solid "clicky-key" (go into that in a minute) keyboard that was made. It's made with a good solid plastic surround and has a metal base to it. It also has removable key tops - making it pretty easy to adjust them to accept the typewriter kets.
The clicky-key bit is fairly simple. "Modern" keyboards mostly use the membrane system of switching. A keyboard is basically a big set of switches - one for each key - that the onboard electronics convert into different electronic signals, which the computer then interprets as a keystroke. So pressing an "A" for example has a slightly different electronic signal than pressing a "B". However it is still basically an on\off switch scenario. Modern membrane keyboards achieve this easily and cheaply by manufacturing a keyboard-size rubber sheet with little "poppets" in it, which - when the key is depressed - make contact with a printed circuit board underneath, thus establishing the contact and thereby generating the signal for the electronics to interpret as a keypress. This is brilliant for manufacturing large quantities of keyboards for very little cost, as the parts are easily assembled etc. However, they don't last very long (as it's normally cheap enough to buy a replacement) as they're not built to!
The clicky-key concept, however, is very different. The keys are individual switches, which connect back through a daughter-board that interprets the switch strokes into keystrokes for the computer. These are electro-mechanical switches and are not prone (unlike the membrane type) to very much wear and tear. The advantage is that they key switches (if neccessary) could be replaced individually and they were designed to have interchangeable covers with the letters\numbers printed on them. So all that, coupled with the fact that they are mounted on a metal platform, lends an air of robustness to the whole keyboard.
And that really is the point! The whole point of the Steampunk thing to my mind is to produce something nice looking, but robust and feeling as if it comes from a Victorian era. That generally means brass and weight! Using the clicky-keyboard goves you the robustness, the quality of build and allows you to add the neccessary brass bits without it falling to bits in a year's time!
So - above is the keyboard in question. I sourced the keyboard from the U.S. from http://www.clickykeyboards.com. Incidentally - the website doesn't just sell the IBM keyboards - they provide a whole technical explanation and history of the keyboards! Even if you don't want to buy, the site is worth a visit, just for a read. I wanted the real thing, so I ordered mine from there. It took a month to arrive and cost quite a bit for postage and packaging (in both Countries!) however the keyboard arrived as new, undamaged and in good working order.
My IBM Model M prior to stripping.
As you can see from the above serial plate, the keyboard was manufactured by IBM on 1st August 1989, which makes it slightly over 20 years old!