When a program steals focus, it will "pop up" in front of the window that you're currently working in on your computer. Windows XP is setup by default to prevent programs from stealing focus but this setting is sometimes changed when certain programs are installed.
Focus stealing is annoying and serves no purpose, unless you have a program that you want a full-screen interruption from on a random basis.
If programs are stealing focus from your current window, follow the instructions below to download, install, and use the Tweak UI program from Microsoft to stop this from happening any longer.
Download Tweak UI. Scroll down the page and look for it on the right-hand side. Be sure to download the program to a location where you can easily find it, like your Desktop.
Note: Tweak UI is freely available software provided by Microsoft. Tweak UI is used to make a number of changes to your system that would otherwise require edits to the registry.
Double-click the downloaded file to install it. Follow the instructions provided during installation.
Navigate to Start, then All Programs (or Programs), then to the Powertoys for Windows XP folder.
Click on the Tweak UI shortcut.
In the Tweak UI program, click the + next to General on the left.
Click on Focus.
On the right, check the Prevent applications from stealing focus checkbox and then click the OK button.
From this point forward, programs should no longer steal the focus from the window that you're currently working in.