It's a Microsoft Windows XP thing, maybe also Win2K. Windows XP really traces everything. It's the widest spread and most often used spy bot worldwide and most users even don't know how many data WinXP collect in background about user activity. Well, the most traces/caches/MRU entries are for increasing speed of WinXP, but they could be analyzed also from a different point of view to generate an user profile. You need a program like SpyBot Search & Destroy to delete those traces.
I delete the whole arpcache key and the files in C:\Windows\Prefetch and many other entries/files once per month. That's not only for deleting privacy data, it's also for increasing speed because the caches increase in size permanently because not existing programs are never deleted from the caches. UltraSentry is a wonderful tool to quickly delete those traces/caches in files and registry. It's only a little bit time consuming to add the files and registry keys to a profile. Don't ask for my profile. Many files/entries include paths different for every user and my WinXP installation is far away from the Microsoft standard. For example I have WinXP eng., but there is no Documents and Settings directory on my computer.
Best regards from Austria