you guys are killin me! scott, as long as you cannot possibly run both the dryer and your whatever at the same time you will be fine they way you have it.
aluminum wire is still used in every new house. for range wire, for your service entrance conductors, both from the transformer and down your service mast. just not for anything else however.
#8 gauge wire can only handle 50A if it is copper and you are using it at 100% of it's rated capacity, not 125% as in if it's for a motor. it's probably easier to find #6 copper romex than #8 anyway.
the size of your circuit is determined by one and only one item: the overcurrent device, ie the breaker. whether or not you will burn your house down is up to you and the size of wire you want to use. try table 310.16 in the NEC and if you have a load that is a motor or on for over 3 hours at a time mulitply your load by 125% (1.25) to size your circuit.
if you put a new dryer (with a 4 prong plug having a nuetral) to an older 3 prong outlet, you will be using a 3 prong cord/plug. the nuetral and ground will have provisions to be tied together inside the dryer at the cord connection. and i have recently found out that yes indeed, both the light, computer AND the motor turning the drum, run on 120V. only the heating elements run on 240.
all circuit conductors are req'd to be run in the same raceway or cable. EMT is considered a grounding conductor with approved couplings/connectors so no need for a grounding conductor (green wire). except from the box to the cord/recep.
what else did you guys post here:
the two hots do have to be under the same breaker. however two 120V (single pole) breakers can be tied together with an approved handle tie if you put them next to each other. if you were hard up for temporary purposes only you could take the hot from two 120v circuits and make 240 happen, but if and only if the hots came from different phases in the panel.
you guys scare me with this one. hire somebody that knows what they are doing.
i used to frequent a dyi forum for electrical work, but i realized i was probably doing more harm that good. i STRONGLY recommend against you laymen doing ANY electrical work at all. some people think that if they can use a screwdriver and have a dyi book that they are electricians. y'aarrrr!!!