There has been few postings about this same subject but they do not provide the answer I need, so here is the subject again.
I have been running office 2007 for few years and now I need to have office 2003 installed as well. I run basic IT courses (funny that) but this is slightly out of my expertice area. A client needs training on 2003 (!!! yes 2003) so I installed a licenced copy on my computer. The probem is that the 2003 version took over my outlook PST file so my outlook 2007 email does not have association with email, which kind of makes sense. Also in the All Programs menu the Office 2003 applications are highlited as if they were the default application. I also had to "reinstall" Word before using it again. The question is; how do I change the preffered or default program back to Office 2007 from 2003, but still leaving 2003 installed and working because I need it for teaching.
Do I need to reinstall office 2007 again so that it takes over from 2003 or run Restore System to go back to status before installing 2003?

When running multiple versions of Office on a PC, you must always do the installations from oldest to latest, in order. Although most apps can co-exist, only one version of Outlokk can be installed & run at any time (when you install a later version, the earlier one will be uninstalled and the user files transferred).

At this stage, I'd suggest uninstalling both Office versions (2003 first), then reinstalling both (2003 first). Your user files & settings should survive the process and function correctly afterwards. Nevertheless, you should always make backups before making significant system changes.

A System Restore should reinstate your system to its pre-2003 state, but you'd still need to uninstall 2007 before installing 2003.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]

Thanks macropod, after trying few things I concluded the same and uninstalled Office 2007 and reinstalled it. Outlook found the old pst file so I got all my calendar and emails back.
One odd thing though, when I start Outlook it gives me a message that there is no email program associated with the application but the email works fine...

Go to Start|Default Programs|Set Program Access and Defaults|Custom and make sure Microsoft Outlook is set as your default email client. Hopefully that will solve the problem.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]

It is defaulted, I have checked that few times during this process. I hope that it sorts itself out after few reboots.
Thanks for help.