I don't know how these got there in C:\Documents and Settings\

I have duplicate folders of:

"Administrator"

"All Users"

and my personal account "User"

At the end of the folder name, is the Computer's name,

eg. "Administrator.Computer.Name", etc.

Anyone know why this is?

This usually happens when you log off an account, and log on again without restarting. Some driver or service had a handle open to the user's registry (ntuser.dat) or a file in the profile (%userprofile%\), causing the profile to fail to unload during the log off attempt. Thus, when you went to log on again, a copy of the profile was created (otherwise the logon would fail), but it gets a different name (usually <user>.00x or <user>.computername (or a combination of the two). Normally, I would state in this situation that you would do well to download and install the user profile hive cleanup utility, but only betas of 2.0 work on x64 (and good luck acquiring it).

In any case, make sure you cleanup the startup items and services on your machine you don't need, as well as make sure your print drivers, antivirus software, and any antispyware / firewall software are also running the latest versions available to you - any of these things can cause this issue.