Thad: I think the relevant quantities in context would be ten or more doubles and five or more boxcars. As far as your calcs go, I think the 10 doubles figure has to be multiplied by the combinations of 10 items chosen from 45, which I think is 45!/(10!*35!). A comparable adjustment needs to be made to the second calc, but I don't have time to work it out :-)
The chance of rolling exactly 10 doubles in 45 rolls is (1/6)^10 * (5/6)^35 * C (10, 45), where C (x, y) gives you the number of ways to pick x elements from a set of y elements. Rolling exactly 5 double sixes, and exactly 5 other doubles out of 45 rolls happens with chance (1/36)^5 * (5/36)^5 * C (5, 45) * C (5, 40).
The former is slightly less than 9%, the latter is slightly more than 0.1%.