cannot install xp sp3 ntdll.dll error

1. While installing Windows Service Pack 3 (and you will install Windows Service Pack 3 coz our dear friend Automatic Updates will prompt you to at some point, typically when you're in the middle of something critical), if you receive the following error, follow the next few steps: "The file c:\windows\system32\ntdll is open or in use by another application. Close all other applications and then click Retry."

2. For the technical minded amongst you, please visit the MS forum. If you're like the rest of us, follow these steps:

a. Shut down all Anti Virus Software (you may have to shut down individual services). Click Retry. If you still get the error, try step b.
b. Shut Down all Anti-Malware Software (such as Spybot, AdAware etc.). If you still get the error, try step c.
c. Clear the contents of C:\Windows\Temp. If some files remain, you need to install Unlocker so you can delete those files. Don't worry - Unlocker is safe. I've used it for years. It's a great little utility to have around when you find your files locked by an application.
d. After installing Unlocker, select all the files in C:\Windows\Temp, right click and select "Unlock All" (figure below)

e. Continue with your Service Pack installation (by clicking Retry on the error window).
f. Every time you get an error about a locked file, use Unlocker to release the file (you'll get about 4 more after ntdll.dll)
g. Abuse Microsoft and Bill Gates (but not too loudly - computers have ears) and get on with your life.