Registries are "files". However, instead of representing things like images, movies etc they generally hold locations, settings records and other data.

Example:
You installed PACreator. The files went on your install folder and the settings (how loud, theme, size on screen, , location where you installed it etc) are going in the registries. So, if I installed a demo of PAC, the next time I reinstall it, he (the program) will search for a previous install not by searching in the installation folder but by reading the registries. If it finds previous installs it will read how many days it is available as a trial. This is how most programs work. There may be some exceptions to tighten the security of the program but in essence the data is in the registries.
Now, in your case, the previous install (the data in the registries) is causing problems to the current install.

Now, just uninstall the program "normally" and follow the the steps that you were suppose to follow.
1. Make a restore point (for backup purpose): http://www.vista4beginners.com/System-Restore
2. click on start button-> type regedit in the search box-> click/enter on result->(the window that opens is the Registry "manager" also called regedit=reg[istry] edit[or] )-> save the registry file (export) ..also for back up reason .. in the top menu of registry editor, click file and see export->... now after doing this export-> follow the path given by the guys at Pyro (left folders in the registry editor window. Click on the arrows, next to the name of folder looking items (HKEY...) or double click on them to expand).
After you have deleted them, close the Registry Editor. You don't need to restart or something like this. Now, try to reinstall PACreator. If it works then it works, if it doesn't work, be sure you have done the steps right (deleted all the files), prompt the Pyro guys for more assistance and tell them the steps they told you to make didn't work.

The "files" deleted in the registry aren't going into a recycle bin, they are deleted permanently (that's why you need to back-up). Also some of the "files" contained in the registry editor are helping Windows to "drive". So I advice caution when deleting a "file" contained in the Registry editor.

Your antivirus&other-defenders deleted a part of the threat called mywebsearch toolbar. Although an easy fix would be to reinstall the program, I wouldn't recommend it. There is a reason your antivirus&co deleted a part of it.

1. Go to Add/Remove Programms. Uninstall the MyWebSearch toolbar if you can find it.
2. Unplug the internet connection and scan your computer.
3. click start->type msconfig->click on the Startup tab/category in the System configuratin window->look for MyWebSearch toolbar-> if found, uncheck it.-> Apply->restart-> see if you have problem.
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4.If you still have the same problem. Save the registry (see my first post)->and search for "m3plugin.dll". When found see if directs to the path that it did before (C:\PROGRA~1\MYWEBS~1\ or the equivalent C:\Program Files\MyWebSearch). If it does, delete it. However as I said before this should be done with caution.

Advices:
a. Be careful when install things like smilies for messenger. After a few searches I found this to be the main cause of your problem.
b. Next time make a new thread with your problem. This way a response will come sooner.

Hope this helps.