UXtheme.dll file is a system file which you have to patch up in order to use custom Vista themes or MSStyles on your computer. To patch up the file, first of all, you need to find out which Service Pack you are running. For this, just press windows key plus Pause or Break key. This open system properties window for you. Then, depands on the service pack you are running, you neeed to download the UXtheme.dll file with which you have to replace original UXtheme.dll file. If you are running Service Pack 1 then get this file. If you are running Service Pack 2 then get this file. Then, just unzip the downloaded file. After this, you need to download another file that is called as Replacer. The use of the replacer is that it safly replace the original system file with the downloaded file. The replacer also helps you to backs up your file in case you need to revert the changes. Now, just unzip this Replacer file to use. Now, double click on replacer file. Then , Go to System32 folder and replace original UXtheme.dll by drag and drop it into the window. After this, Open the folder with the downloaded file and drag and drop the file into replacer. Now it will ask you to confirm that you want to replace the files or not. So double check and then press enter. Replacer will now swap your original System file with the downloaded one. Now restart your computer.That's al done!!