Can't perform operation - default mail client is not installed properly.

I use windows XP and my default mail client is Microsoft Office 2003 and everythying was working fine until I came into my room and noticed that my son had decided to download a trial version of Microsoft Office 2007, (without my permission). I removed Office 2007 and re-installed my Office 2003 disk. Immediately my email popped up with all of my old messages and everything in it, however, now, whenever I try to send an email from someone's site online, I get an error message stating that "The operation cannot be performed because the default mail client is not installed properly." Microsoft Office 2003 is my default mail client and it is the one I want to be my default mail client. I don't know how to change anything about the installation of it. Help, please.

 

Thanks Arie. That works fine up to the point where you instruct me to Enable access to this program for Outlook 2003 however, Outlook 2003 is not one of the choices. The choices are "Outlook Express " and "Use my current email program." Right now, I have "use my current program" enabled.

 

It is already set up that way.
Would it help to roll back beyond the day that he installed the Office 2007 trial, or perhaps to reinstall my entire windows xp or use my system restore disk and reinstall my hard-drive? That seems so drastic.

My harddrive was recently restored because it crashed after a power surge and destroyed everything on it. I purchased a new hard drive and used my system restore disk and got my pc back but certain drivers did not reload such as my cyberlink power dvd, and certain codecs etc. (now I cannot view a dvd on my pc) certain software won't even download or load/install properly since purchasing the new hard drive and that is strange because other times I used the disk when the hard drive went out and it restored EVERYTHING just like a new pc, but anyway, that is a whole other problem.

 

I would have to agree with you about that because I have several issues with some of my other programs involving the drivers, software and other performance, however my email was working absolutely fine until my son downloaded the trial of office 2007 and then all went haywire.