Any suggestion for lightweight bitcoin wallet program?
You can imprort private keys to Electrum wallet. Use "electrum importprivkey yourprivatekey" command.
Great, I found elecrum and I was looking for this command right now. Thank you.
Here is tut how export private keys from satoshi client
http://bitcoin.stackexchange.com/questions/4203/how-can-i-export-the-private-key-for-an-address-from-the-satoshi-clientTo export a private key from your Satoshi bitcoin-qt client:
launch your bitcoin client as usual and wait for it to load the blockchain and start up
click on 'help' in the menu bar (top right)
click on 'debug window'
select the 'console' tab
type: walletpassphrase "your walletpassphrase here" 600
type: dumpprivkey [your public key here]
this will return the private key, you can copy it now; ensure you clear your clipboard/history afterwards
type: walletlock