Question : Transition or Restructure 2003 to 2008 R2 AD? Migrate Exchange 2003 or just move to 2010?

We are doing a hardware and software refresh and would like to end up with new 64 bit servers running 2008 r2.

Currently on a 2003 domain with Exchange 2003 (latest sp's applied to all). My question is how best to arrive at the end goal of a 2008 r2 domain with Exchange 2010. We are also wondering what the best pratice would be in terms of tranistion vs. restructuring. We are flexible in that we could either retain the forest or build (restructure) a new one.

Would like to minimize risk and downtime to this site of roughly 100 users. Forest, Domain and Exchange are all operating at native modes. We are leaning towards restructuring as that would allow us to change the domain name to something more desireable.

Answer : Transition or Restructure 2003 to 2008 R2 AD? Migrate Exchange 2003 or just move to 2010?

First off, I'd recommend a migration vs a new build. Unless you truly suspect problems with AD, the impact on end-usersis much less significant with a migration. New builds always introduce unexpected and unwelcome security permissions issues as old SIDs stick around on files in unexpected ways.

Even if you want to rename your domain, you can migrate the user accounts and data via ADMT.

http://technet.microsoft.com/en-us/library/cc974332(WS.10).aspx

As far as Exchange goes, since it sounds like you'll be doing a hardware refresh as well, that makes things easier as both machines can exist at the same time. MS actually has a lot of documentation on upgrading your infrastructure to Exchange 2010 from 2003.

http://technet.microsoft.com/en-us/library/dd638187.aspx

In short, with only 100 users, this should be a pretty straightforward migration. As every environment is unique, I obviously cannot gaurantee that, but I saw nothing in your post to make me overly concerned. Just a matter of planning, documenting, and then executing.