Yes, your old wallet will work in the new client if you just copy your wallet.dat from the old data file to the new one. Just to be paranoid I'd recommend backing up both wallet.dat files elsewhere before overwriting the new wallet.dat with your old client's wallet.dat.
Of course, your wallet should already be backed up elsewhere anyway, but an extra backup until you confirm the balance visible in your new client is as it should be doesn't hurt.