Mid Plains,

I do a lot of 14er climbing here in Colorado and you will adjust to the altitude in a day or two. The best way to avoid the headaches/nausea associated with altitude sickness is to drink plenty of water. You won't be thirsty, but drink anyway. The higher you go, the drier the air and the more fluids you need to intake. You can also take some motion sickness pills (I prefer Bonine) to help alleviate some of the discomfort, but that should not replace water. Did I mention drink lots of water?