Hi,
I have doubt about WEP(Wired Equivalent Privacy). Can I use 4 differnet keys(40bit key,64 bit key,40 bit key,128 bit key)to encrypt the data? all these keys should encrypt one particular data, so is it possible?

No.
Only one key is going to be used.
It just happens that you can configure 4 different keys that the router can use ... but the client only negotiates one of those 4 to use.

thank you friend... I have another query...

Can you tell me about Distribution system?

Hmm, not sure what you mean by that.

Also note that the 40bit key is generally the same thing as the 64bit key. WEP uses a 24bit initialization vector (IV) that is concatenated to the 40 bit WEP key (40+24=64). Same applies to 128bit keys, they are actually 104 bit keys with a 24bit IV.

Also, I would not use WEP for encryption. WEP is an extremely poorly implemented encryption scheme and it's possible to sniff wireless traffic for a few minutes and extract the WEP key, thereby allowing you to decrypt packets. If you need encryption use a more secure protocol or at the very least use something like ssl (either as in https or ssl tunneling). WEP is really only useful for keeping the casual person from piggy-backing off your LAN.