Per the USB standard 500mA at 5V per port. Sounds like you are pretty maxed out as it is, but I did open mine up and reviewing the pictures I took, it looked like Maxan put in a PTC "resettable" fuse. They are nice because they don't break then just increase current limit until the load is removed. They are fairly inaccurate so you might get more current out than the 500mA. The best thing to do is to get a current meter and measure how much current you are using now and then measure the hard drive alone. Add the two up and if it is significantly over the 500mA you are probably in trouble and will have to distribute the load across other ports or power the hub externally.
