If I install the bitcoin command line client for linux, can I use just a public and private key to send coins from an address? I don't want to add it to my wallet file, I just want to move coins out of an address.
Update: After reading some of the answers I realize that I should have been more clear about my purposes. This is for more of a computer controlled money system. I want to be able to create addresses, and move money between them, and be able to move money out of addresses to other public addresses. I wanted it to be super light weight and not have to download the whole block-chain to achieve anything, and I don't want it to use wallets because they don't conform very well to what I am doing.
I want to be able to be given a private key and public address of a source, and a public address of a destination, to be able to send coins from one to another, and do it by just sending a message to the network. I want to be able to do it with only 10-20 MB of storage, and be able to do it by only connecting to a few nodes. Confirmations & balances will just be handled by hitting up some public resource like blockchain explorer.
Note: if it is not possible to do without the blockchain handy, then that can be accommodated for (though it throws in the need for a server for me rather than being purely client based.).