I was going to do my 293 but I deviated as I have been labbing Exchange for the last month hard and using the beta on and off for a while now. I have heard alot of powershell command questions are on there so hopefully I can reason them out as I doubt I will have everything memorized that they are looking for..
I am using "How to **** at Configuring Exchange Server 2007" which is a very good read since its made for humans.
Microsoft Exchange 2007 Unleashed , reading online at Safari, its been pretty good and in depth, I think there are a few errors however but overall it seems good more for concepts and not EMS.
Most importantly, spending hours reading the get-help * area of the powershell... This to me is pretty much the only way you will be able to learn in a way that suits you well. I currently have a lab at home and at work, for a machine at home I am using a 3800+ with 2 gigs of ram and have 2 instances of Exchange running using VMWare, it works well since theres not alot hitting it other then me

I will let you know how I do... Hopefully I will come out a new MCSA/MCTS