Subjects in Part 1 (Dose Finding Phase) Only: The overall goals of this study are: (1) to compare the effects, good and/or bad, of a new combination of chemotherapy using VAC/VI plus temsirolimus; (2) to find if adding the drug temsirolimus to VAC/VI therapy will get rid of the cancer better than VAC/VI by itself. Subjects in Part 2 (Regimen A and Regimen B Randomization) Only: The overall goals of this study are: (1) to compare the effects, good and/or bad, of a new combination of chemotherapy using VAC/VI plus temsirolimus; (2) to find if adding the drug temsirolimus to VAC/VI therapy will get rid of the cancer better than VAC/VI by itself; (3) to find out if adding maintenance therapy after VAC/VI therapy with or without temsirolimus will get rid of the cancer better than VAC/VI by itself. Patients Eligible for Regimen C, VAC/VA Only: The overall goal of this study is to see if a shorter length of treatment and lower doses of cyclophosphamide used together with current standard doses of vincristine and dactinomycin can be as effective in curing subjects as using the current standard doses of all three drugs, and cause fewer late effects.