There is no way you can use / spend / get those bitcoins without having access to the wallet (or the private key, or import it).
What is this private key you speak of?
Blimey, I suggest you read up on addresses and wallet security before you do anything with any coins. Every transaction in your wallet has a public key, which is what you see all over the place, and a private key which only your wallet 'knows'. If your wallet gets lost/deleted/reformatted then you can not do anything with the coins associated with that key. Nothing, nothing at all. They are lost.
Make a backup of your wallet, then make another backup onto a different medium. Then put the backups somewhere safe.
There is a wiki post on security - read and understand.
('Wallet' is a misnomer. The coins are never 'in your wallet'. The record of all the coins and all the transactions are in the block-chain, the wallet only holds your keys, so that it can pick out your transactions. If someone gets hold of your wallet or private keys, then they get control of any coins associated with that key, even transactions in the future. If you think your wallet has been compromised, get a new one and never, ever use the old one again.)