Once you have downloaded this file, extract it to your local drive (c:\) so you can access it later.
Restart your computer and get it into safe mode. (To get into safe mode repeatedly tap the "F8" key after the bios screen fades, a list will come up and allow you to choose an option. Choose "Safe Mode", once booted, select your account, then press "yes" on message box)
Once done guide yourself to where the file is through explorer in "C:\windows\sytem32"
Look for the file and select it. Now since it is a required windows file it will not allow you to delete it, but a little trick is you can cut and paste the file. So select the file>right click on it and choose cut. Paste the file in a new folder on your c:\ (eg. C:\infected) With the file you downloaded, copy and paste the new wininet.dll file to "C:\windows\sytem32".
Almost there, restart you computer and start it up normally. Go to c:\infected and delete that infected file.
Just for good measure, run a full scan on your computer and make sure it is virus free.