MSI Hell

Recently I bought some new software. When I try to install it though it says it can't recognize the MSI file and stops the installation. I GREATLY preferred the days of setup.exe. I looked on google and found that MSI is Microsoft Installer file. Leave it to Microsoft to find another way to make windows users lives complicated, difficult, and their operating system something I wish I'd never become involved with. I don't have any corrupted files and I checked and I do have MSI 4.5 version on my computer but it can't recognize the MSI files in the software I am trying to install. My own guess is that my Webroot Antivirus with Spysweeper is the problem causing culprit but I have no way to prove that. Everything I read about how to fix it is like looking at a diagram from NASA. It is really really complicated and involves playing in the registry which can mess your OS up fast!!!!!! I am at my wits end trying to find a way to get my machine working properly again. I have HP Pavilion computer with Vista installed on it. Can any of you saavy techies out there please assist me? Thank you.

Well i have got a solution for you, just follow the simple steps that i have given below and i am sure that will solve the problem.
1) First go to start and then go to run, now type regedit, now select ok.
2) now you have to find out and locate the following registry key that i have specified here
HKEY_Local_Machine/Software/Microsoft/Windows NT/CurrentVersion/Winlogon
3) Having done that right click on the right pane and then in the AllocateCDRoms, you will have to select Modify.
4) Now you will get the Value data box type in 0 and click on OK.
You are done.