What you will need:
Overview
One use for web based audio is to give your students an audio record of your lecture. It is not necessarily a replacment for a live lecture, but can help students that may have missed a class catch up, or give students a way to review content before an exam. It is not particulaly hard to do.
Computer, Laptop or Recording Device
Nothing too powerful needed here -- a P166 or better should be able to keep up, if that is the only application you will be running on this machine. If you plan on recording in the background, while using the laptop for presenting, you will need something a bit more powerful, perhaps a PII-266, or a G3 PowerBook or better.
You will of course, need audio inputs on your laptop, most come with line and mike inputs. Note that Apple's newest laptops *do not* have audio inputs, so you will need to buy an audio input device. Griffin Technology's iMic will do the trick, or you may want to look at semi-professional USB audio devices -- some of these come with a microphone preamp built in --- very handy.
You can, of course, just use a portable tape recorder or minidisc recorder to archive your lectures as well. Avoid temptation to use C120 or C160 audio cassettes; the tape is very thin, and will not hold up to much use/abuse. I recommend not resusing regular audio cassettes more than 10 times -- unless you have a bulk tape eraser -- tapes will become more noisy after multiple record/erase cycles. BTW -- this is true for VHS tape as well.
Wireless Mikes
It's easy to spend a lot on a wireless microphone; the state of the art UHF microphones, that are impervious to much interference and signal fade start at around $480. VHF microphones are usually cheaper -- single channel models start at around $180 for a kit (mike, transmitter and receiver). The next step up is a model that is VHF, but broadcasts on two frequencies (known as diversity mikes). These are more resistant to signal fade, and are well worth the extra expense.
Sample Mike Systems
Nady Silver 332 with a lavaliere mike $220 (true diversity)
Nady Duet (2 Mike System) $339
Samson UHF Synth 32 Omni Lavaliere Mike $479
These are all fairly cheap, but decent systems. You can always spend a bit more and get well known brands like Shure, Sony, Sennheiser, etc.
Audio PreAmp
While many wireless microphones boast line outputs, it is often that the signal strength is not enough to drive a computer's mike or line imput. This is where a mike preamp helps. It will boost signals, and gives you a standard audio interface that most wireless mikes use. Most importantly, they have real knobs that can make set up that much easier.
MidiMan makes a fairly inexpensive one that is up to the task:
http://www.midiman.com/products/m-audio/audibudy.htm
You can also use an inexpensive mixer. Radio Shack sells a inexpensive 4 channel mixer for around $70.00.
Recording Software
By far the easiest way to accomplish archiving a lecture is to use the free version of RealMedia Encoder, available for both the PC and Mac. It will record your audio in real time and give you a RealMedia file as a output. The biggest disadvantage to this approach is that you will not be able to reedit your audio file with standard audio tools; you will only be able to accomplish simple edits with RealMedia Editor -- which is very limited in what it can do (essentially, trim pieces, or append files).
Here's a link for RealProducer Basic:
http://www.realnetworks.com/products/producer/basic.html
If you have a fair amount of drive space, you could instead choose to record your audio using a standard audio recording package, such as CoolEdit 2000, or Peak LE. In particular, on the Mac, Coaster is a great, simple audio recorder application that can run in the background:
http://www.visualclick.de/products/coaster/index.html