It's hard to tell how fit you are now - so I'm not sure what "evening exercise routine" would entail. It may or may not be enough. It sounds like you aren't experienced with altitude, but I can't tell if you have experience backpacking at lower elevations.

Ideally you should be in good aerobic shape and fit enough to walk long distances with weight on your back before you leave home. If this means working out on the stairstepper 30-40 minutes a day, and doing 8-10 mile hikes with 20 pounds in your daypack on the weekends, I'd recommend starting that. I think that 8 days at altitude before you start the backpack trip should be plenty of time to acclimate to the altitude alone, if you are already aerobically fit (I usually try to get one or two days at altitude before the backpack trip if I am already fit). It may help to do a few day hikes during the 8 days, especially if you can go up two or three thousand feet higher than the starting point. Even if you can drive up higher and hike there before coming back down to sleep, that helps with acclimation to altitude.

You still may want to take it easy the first day or so once you start the trip. Once you start to get that high-altitude headache and/or nausea, it's no fun, and it doesn't go away easily. If you prepare well for the hike, hopefully you can avoid any such symptoms. I once made the mistake of driving from sea level to 8000 feet, then going on a hike up to 10,5000 the same day, so I know whereof I speak <img src="/forums/images/graemlins/tongue.gif" alt="" /> Spent the evening in a fetal position in my car till the aspirin took effect. <img src="/forums/images/graemlins/frown.gif" alt="" />

I second the comment about keeping hydrated - the rule of thumb is to drink enough that your pee is clear (not yellow or darker).

Do make sure you're prepared, and you should have a wonderful time!