How can create individual wallet for each user I am going to develop an exchange website in PHP something like http://coinbase.com, 
Now, I have setup the http://bitcoindevkit.com/ for it and its running fine generating new addresses in the same wallet,
but now I need to create a individual wallet for each user, so how can create individual wallet for each user and then I can able to create address on that wallet.
I would suggest using the bitcoind Account feature to track the different user 'wallets', this way a single 'wallet' or account can have as many address's as required which can all be be accounted for to that named account.  However I would also suggest not having this on your actual server, use a database to mirror what the bitcoin client shows, and hand actual withdrawals manually, (at least the larger ones) you may want to have a bitcoin daemon linked directly with a small amount of float to handle incidental day to day transactions.