Upgrade Windows 2003 Standard to Enterprise (In-Place upgrade)

I am checking to see if in-place upgrade is available from windows 2003
standard to enterprise. If we do so, will data (it's a SQL server) be
preserved or such in-place upgrade is not suggested, or too much risk?
Thanks for the advise.

No problem. Doesn't hurt anything that I've encountered. Just can't go
backwards. I know that if you want the clustering capabilities of
Enterprise, and assuming that is why you are installing it, you would have
to install a cluster aware app, such as SQL or Exchange after the cluster is
setup so the app is aware of the cluster and will install the app's cluster
DLL versions. If it is for more memory, then I wouldn't worry. Just alter
SQL's memory configs.

Can I upgrade Windows Server 2003 Standard Edition to Windows 2003
Enterprise Edition?
http://windowsitpro.com/article/arti...e-edition.html

I forgot to add as my own advocate, I've always performed a fresh install of
all OSs and have never upgraded an OS due to unknowns and bringing over old
stuff. If you are not sure, I would suggest to install it fresh and install
a fresh copy of SQL and migrate your data. This way you are working with a
"known."

I am doing an in place upgrade from Server 2003 Standard to Enterprise. The server receiving the upgrade is a domain controller. This is probably a stupid question, but what will be affected as far as my company's access to email and login while the upgrade is happening? I'm going to guess that it will be down, but I wanted to make sure.