EDIT 2/15/2010: Please see this post for updates on this subject.
We always talk about listening to customers and sometimes this is written off by many as 'marketing speak'. In fact, we do take ...
Updated Jul 01, 2019
Version 2.0
Blog Post
@idiegoit
If you can't possibly find another server somewhere to install Exchange on, then I would recommend then installing a Hyper-V guest OS VM on your DC, and installing Windows 2008 SP2 (not R2) in that VM with Exchange 2007 SP2. This will allow you to run on the same hardware with out running into conflicts between Exchange 2007 and Windows 2008 R2.
A few words of caution with this design though, you need to make sure you have enough processing power to do both, and enough RAM to split between the VM and the host. Disk speed should be the same regardless as you would have been using the same disks either way. This does add the complexity of understanding and managing a Hyper-V installation though.
Meanwhile a reminder to everyone - it is not supported to install Exchange 2007 on a DC that isn't also a GC:
http://technet.microsoft.com/en-us/library/aa997060.aspx
Generally though it is not recommended to install both roles on the same server.
If you can't possibly find another server somewhere to install Exchange on, then I would recommend then installing a Hyper-V guest OS VM on your DC, and installing Windows 2008 SP2 (not R2) in that VM with Exchange 2007 SP2. This will allow you to run on the same hardware with out running into conflicts between Exchange 2007 and Windows 2008 R2.
A few words of caution with this design though, you need to make sure you have enough processing power to do both, and enough RAM to split between the VM and the host. Disk speed should be the same regardless as you would have been using the same disks either way. This does add the complexity of understanding and managing a Hyper-V installation though.
Meanwhile a reminder to everyone - it is not supported to install Exchange 2007 on a DC that isn't also a GC:
http://technet.microsoft.com/en-us/library/aa997060.aspx
Generally though it is not recommended to install both roles on the same server.