Peace be upon you!
1-Do I need the Arduino mega or Duemilanove kit side by side with the
Arduino BT Kit?
2-Does the Arduino BT Kit supports iWrap2 or iWrap3
i.e. the bluetooth module inside the Arduino BT kit is WT11-A-AI or
WT11-A-AI3?
3-Could I easily replace WT11 in the Arduino BT Kit with WT41 ?
4-Arduino board is better or equal to Evaluation kit from bluegiga?
Please I would Appreciate any help 
Hello Profvip,
1-Do I need the Arduino mega or Duemilanove kit side by side with the
Arduino BT Kit?
No but will be handy if you messed up the WT-11 Configuiration.
2-Does the Arduino BT Kit supports iWrap2 or iWrap3
i.e. the bluetooth module inside the Arduino BT kit is WT11-A-AI or
WT11-A-AI3?
Google: "Arduino BT as a BT Keyboard "
3-Could I easily replace WT11 in the Arduino BT Kit with WT41 ?
No very hard unless you are extremely skilled in using 2 soldering irons simultaneously
4-Arduino board is better or equal to Evaluation kit from bluegiga?
If you are after making your own keyboard, the best route would be to purchase the following
1 http://www.semiconductorstore.com/cart/pc/viewPrd.asp?idproduct=5101
2 FTDI Basic Breakout - 3.3V - DEV-08772 - SparkFun Electronics
3 http://www.sparkfun.com/commerce/product_info.php?products_id=9220
Remember it is very important that you "learn" how to communicate with the WT Module directly using serial communications, you can achieve this by putting together #1 and #2 read the specs and carefully solder the wire for the RX TX VDC and GND of the WT bluetooth module to the TX RX VDC and GND of the FTDI break board.
Also just to note, combining #1 #2 #3 will save you cost and save you the effort of updating the firmware (Arduino BT has an older firmware that does not support HID profile) I preferred to just get the cheapest BT Module from bluegiga that has the HID profile.
Hope this helps!
;D