I upgraded iTunes through the regular software update without issue. One thing to consider is that it may be a good idea to download and install each update one at a time (for example 10.6.3 first, then itunes, then airport update, etc.). A few people have reported issues related to installing multiple updates that require restarts at the same time. I can't say for sure that this causes the problem, there are just a few anecdotes around. I didn't plan to do it this way, but I installed them seperately and restarted after each. Couldn't hurt to be overly-cautious. Of course, having a solid backup plan is always the best option.