Your client just hasn't downloaded the blockchain yet. You can always check what the latest block number is, for example here:
http://blockexplorer.com/q/getblockcount. (Roughly 230k blocks right now.)
Alternatively, you can install a newer client but keep your wallet.dat. As soon as the blockchain is downloaded your funds should be visible. Just remember to guard that wallet.dat with your .. well, guard it well. Multiple encrypted backups, at the very least.