Does archos 28 has a built-in speakerphone? And what was the use of its microphone?

1. Connect the supplied USB cable to the ARCHOS.
2. Plug the USB end of the cable into your computer.
3. The ARCHOS will turn on and ask you if you want to connect it (Mount) or not. Choose to Mount it.
4. If you choose to just let it charge, you can always drag the top notification bar downwards to reveal the USB notification message and choose to connect.
5. The ARCHOS will appear in your computer's file browser as an external hard drive, ARCHOS (E:) for example.

More Information & Instructions about your Archos 28 here:
http://www.archos.com/manuals/A32_EN_v1.1.htm#zzee_link_1_1294043188

Look at the back of your archos 28 to indicate or the receipt.

the same thing happend to me !!! what do we do

You can connect you Archos to you computer by the USB cable which have came along with the tablet.
From tablet you need to choose mass storage device when you connect the cable. Once Mass storage activated you will see your tablet or SD card on your computer. You can copy paste or drag and drop songs from your computer folder to archos tablet Music or Media folder.
Or
You can use various Sync application from Android Market. Below given link is to list of applications available on Market. Please read description before you purchase or install any application.
https://market.android.com/search?q=itune&so=1&c=apps

Ebay another tablet.

From the Archos User's Manual.

- Press and hold the power button until the ARCHOS banner is displayed and then release it.
- Press the power button twice (like a mouse double-click) while the banner is still displaying.
- A white Recovery screen should appear within a couple of seconds.
- To move from one option to another, press the power button. To select the highlighted item, hold down on the power button.
You'll want to select the Format System option.

Here is variety of docking station and universal mouting for your Andriod Palm tablet PC Notebook, http://www1.shopping.com/docking-station-Archos-28-Internet-Tablet-4GB-Android-Palm-sized-Tablet/products?CLT=SCH#

you can get skype for Android here http://www.freeware4android.net/archos-28-internet-tablet-4gb-8gb-device-1663/skype-android-download-17736.html

My son and daughter got a new Archos 28 each for Christmas, my son's has stopped charging. I of course can not find my receipt and Kmart wont take it back. How else can I get this fixed? I paid too much money for this thing for it to stop working in just a couple of days....Can anyone help me?

Yes! that would be the easier solution to go back and have it exchanged, because if you attempt any kind of repair it will void your warranty.