The reason for the error is I think, like me, you already had a version of Netscape 9.0 installed. It appears to run fine if you are upgrading say from version 8.0 but because this version of 9.0 has a little extra weather bar added to the bottom, it is causing problems. If you don't want this feature check elsewhere in the post for tips on how to remove this too. Is quite easy to do.
The reinstall should pick up your existing version 9.0 profile as this remains untouched after the uninstall. I had no problems with mine but as a precaution do a copy of the folder just in case. It should be located on your C drive under Documents and Settings. Find your profile in the sub directory...should have your first name as the title. Then click on the Application Data folder. Look for the Netscape directory...this is where your profile is located. Do a right click and copy this folder to your desktop. You then have a backup just in case. If all goes well with the reinstall you can then delete this copy from your desktop.
With regard to the other versions you can probably delete 8.0 ok using the add and remove process I mentioned before as this is a standalone browser and won't affect e-mail settings or your main 9.0 profile. With 7.2 I would be more careful. By the sounds of things you are using this for your e-mail package. Although you probably keep telling Navigator 9.0 to be your default browser, everytime you open an e-mail in 7.2 it is going to the 7.2 browser by default. The only way I would say you can get around this is to upgrade your e-mail software. Although Navigator 9.0 is browser only plans are under way to add an improved e-mail client called Mercury. It will be a case of watch-this-space and is still very early on in the development process. In the mean time I would suggest Thunderbird which is the e-mail sister program to Mozilla's Firefox. It is very good and would upgrade your e-mail package safely and easily. You can download it from here -
download
and it will actively look for all your e-mail settings, messages and address book details while installing itself. I use it myself and can recommend it. If the installation goes ok you can then delete all of the Netscape 7.2 program as you will now have e-mail with Thunderbird and your Netscape version 9.0 browser. These are the packages I use and if you click on an e-mail link from Thunderbird it should open up Netscape 9.0 ok...providing you make both of them your default packages.
Finally, with regard to Internet Explorer etc and going to Outlook Express to e-mail something through a link. This often occurs when default settings are not quite setup correctly. Apart from what I have suggested above I would say go to Control Panel again. Look for the Internet Options icon...click on this and this will configure options for Internet Explorer etc. Go to the Programs tab and select E-mail as Netscape 7.2 or Thunderbird if you install it. This will then mean that whenever you click on an e-mail link in Explorer or even Netscape your preferred e-mail program should open up.
As with anything PC it is a bit trial and error but this should work for you as I have the same settings on mine.
If you're still having problems then just post again and I will have a look for you.
Sorry for the long post but I hope the info helps...Best of luck!!!
[Another BBCode edit. profman, 10/13/2007]
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.8pre) Gecko/20070928 Firefox/2.0.0.7 Navigator/9.0RC1