You need to replace the rack assembly. The boot is just to keep dirt off the inner tie rod. There is a seal that you cannot see that keeps the fluid in(which has gone bad). If you replace just the boot it will fill up with power steering fluid because the other seal is bad.

If you replace the rack you should flush out the whole system and install an inline magnetic filter if possible.

Replacing the rack yourself may not be too hard depending on your skills. Check a good manual to see if it makes sense or not. Wheel alignment will be necessary and if the car has an airbag in the steering wheel loop the seatbelt through the steering wheel and latch it to prevent damage to the clock spring(contacts behind steering wheel for the airbag).