As for the "type" of 26" wheels, there's only one common size (559mm bead seat diameter) referred to as 26", so unless you want to play around with mostly-obsolete sizes (and at that point you might as well get 650B wheels), that's what you're using.
If it's designed for sidepull brakes, you might be able to make it work by using longer-reach brake calipers than it was designed for, as 26" and 650B are 559mm and 584mm bead seat diameters precisely, meaning the braking surface of the rim will be 12.5mm lower with a 26" rim than with a 650B, easily within the range of longer-reach calipers assuming it doesn't already use long-reach ones. If it has cantilever bosses, the difference in rim diameter will potentially be sufficient that the brakes won't work, but that depends on the design of the brake and the precise location of the brake bosses on the frame. Disc and other hub-mounted brakes will work fine.
If you haven't already got the wheels, there are plenty of 650b wheels or rims available.
Last edited by Airburst; 09-11-14 at 05:45 AM.