Using Oracle Enterprise Manager

) Is it possible to use a newer version of OEM to manager older instances?

I think you are talking about OEM client, Yes you can manage the older instaces by OEM 11g Client.

2) Is there an installation available for OEM to be installed on Windows that manages AIX Oracle instances?
Yes, install OEM 11g Client at Windows based system and manage AIX Oracle Instances.


3) If possible how does that work?

Install OEM client at windows and create tns aliases for databases installed at AIX box(es) in the tnsnames.ora file.

Where would I find the OEM 11g Client? I can't seem to find an download\install for that product.

http://www.oracle.com/technology/software/tech/oci/instantclient/index.html

explore the following link to see the Oracle By Example Series

http://www.oracle.com/technology/obe/11gr1_db/index.htm

Especially the  following one
http://www.oracle.com/technology/obe/11gr1_db/manage/dbconsole/dbcontrol.htm

I'm sorry but I don't see a download to just install the OEM Database management piece. I'm only wanting the management piece. Forgive me if I'm just missing it.

signup at otn.oracle.com , membership at oracle technology network (otn) is free

then open the following link

http://www.oracle.com/technology/software/tech/oci/instantclient/htdocs/winsoft.html

and then click at the "accept" link and then click at "instantclient-basic-win32-11.1.0.6.0.zip"

and provide the user name and password if it's asked

unzip the downloaded file and install it at windows based system

Enterprise Manager 10g Grid Control (to manage multiple databases at one place)

http://www.oracle.com/technology/software/products/oem/index.html

an other option is web based enterprise manager

Enterprise Manager 10g Grid Control (to manage multiple databases at one place)

http://www.oracle.com/technology/software/products/oem/index.html

or

you can use "toad for oracle" to manage your databses

http://www.softslist.com/download-10-13-27498.html
http://www.download.com/Toad-for-Oracle/3000-10256_4-10597467.html

In SQL Server I have an installation of SQL Management Studio\Enterprise Manager that I have installed on my pc. It is connected to multiple sql servers in our environment. I can use this to create tables\add users\changes schemas\ etc... I'm looking for this same tool Oracle provides to work with there databases. I was of the understanding that it was OEM or Oracle Enterprise Manager. The one I'm using is a web based software running on a Unix box. I would like to have this same software installed on a Windows machine that I connect to to manage all of my Oracle instances. I'm assuming this link http://www.oracle.com/technology/software/products/oem/index.html is the correct place to get this based on the comments you've made. I'm downloading that right now and will install to see. Not sure what the "Grid Control" is and also the latest version of OEM is 11g. I found that by downloading the trial of the 11g Database and when installed it also installs the 11g OEM. I don't see a download for the 11g version. Maybe it's not released like that yet.

Thank you so much for your patience!