Yes, brake pad replacement and rotor resurfacing is an important safety feature, as is tires with adequate tread. I recommend at least replacing two tires and later replace the others as your budget allows you.
A brake system really does not have much to do with the condition of the tires. Although tires create traction and friction on the road surface, brake pads or shoes actually grab the rotor or drum respectively. If your vehicle is in need of brakes, it is best to replace them as soon as possible for safety reasons. It is best to replace the tires however so that when you apply the brakes the tires will grip the road surface.
〉 Answered on Feb 26th, 2009 by Suzanne Grego, Technician at City of Philadelphia Fleet Management