DiffView is a very small (71KB) portable tool which can scan your system to detect and display recent changes to your system files or Registry.
File and Registry trees make it easy to choose exactly what you'd like to check: your User folders, say, or the HKEY_LOCAL_MACHINE\System keys.
And you can choose how recent any changes should be, too. Enter "5" in the "Diff time" box, say, and the program will only look for items which have been created or modified in the last 5 minutes.
With the configuration done, all you have to do is click "Scan files" or "Scan reg", depending what you're doing, and wait for the results. This can take a while if you're scanning the entire Registry - so you might want to tag an extra 5 minutes onto your "Diff time" figure to make up for that - but be patient, it will finish eventually.
And once the process is complete, DiffView displays a tree view report of your system, instantly highlighting any recent changes in the areas you've specified.