rhenning is correct. It is a Giant-built Schwinn Collegiate, so it should take stock 26 x 1 1/38 tires (650A or 590). There were a few made with 24" tires, but they're rare. No need to buy special Schwinn tires.

As far as the hub, I can't remember if it has an oil port on it. Is it a 3CS hub?