The answer is YES.  You can mix them both up. However, if you have ever done this, you will note both these medicines come in individual amps with 3cc of normal saline (water) each.  If you mix them up the breathing treatment will last a long time, like about 20 minutes.  The reason is because you are breathing in the medicine along with 6cc of normal saline.

If you want to speed up the time spent taking a breathing treatment, ask your doctor to write you a prescription for Duoneb, which is a combination of Albuterol, Ipatropium Bromide, and 3cc of normal saline (water).  This way you get all the benefits of both medicines in less than 10 minutes.

For the record, these two medicines are also combined in an inhaler too.  It's called Combivent.