Unlike Windows XP, Vista actually shows thumbnails for each application that you are running so that it is easier to identify what you’re looking for. And they just aren’t screenshots either like a lot of the imitators in XP, instead they show live previews of the application. Overall.
This site which gives some registry settings that you can modify to change the width of each thumbnail, and ultimately the size of the Alt-Tab display. To change the size just download this registry file, and after it is on your computer, right-click on it and select Merge. This will import it into your registry using the values I’ve specified in the file (optimized for displays that are 1680×1050).
The first thing you might want to do before Merging the file is to open it in Notepad (or any text editor) and adjust the MaxThumbSizePx to match something close to your resolution.
1024×768: MaxThumbSizePx = 00000078
1280×1024: MaxThumbSizePx = 0000009E
1680×1050: MaxThumbSizePx = 000000d2
1920×1200: MaxThumbSizePx = 000000f5
If you don’t like how it looks, and don’t want to mess around with it, you can always revert back to the old Vista Alt-Tab dimensions by removing the following “folder