Hi sam
it's not the windows 7 software that controls that it is always unbalanced due to using the collision transfer method of transport system, it really is a question of hardware if the processors and ram are not exactly the same then the faster or the one with more ram will win out.
so you will always have unbalanced down load speed. back in the old days when the token ring method was used yes you could determine the amount and speed of data to each individual computer but with the collision method and the function used to apply for data this method can not be used.
you need to read about protocols relating to internal Lan's to understand this technology as mentioned in the RFC's documents.
this goes back to the days of windows 95.