Doing my pre-purchase planning for my first Mac product (MBA). All of the programs and utilities I use are available in a Mac platform with one exception...MS Streets and Trips. I used this route planning program for years and it works great for me so I don't want to give it up. It gets used during my many motorcycle trips and also for off season planning but in totality it's use is a very small percentage of my computer time. I want to keep the max of the MBA resources during the computer use so I have sort of discounted Parallels or other like software. That left me with Bootcamp but it does mean carving out about 40 gb for Win 7 and the program etc. I did read some threads on using an external USB3 drive. So for those who know.....to have access to use one MS program infrequently what is the recommended option?