The $NtUninstallKBxxxxxx$ folders and associated files in these
folders are created during each Windows Update that is installed
on your PC and are safe to remove if you do not plan to uninstall
any security or hotfix updates.
However once deleted you will no longer be able to un-install
a patch or update that was associated with the deleted folder/files.
I would keep the most recent set (last two months just in case) of folders
and delete the older updates.
Note: As a safety net I burned these folders to a CD before deleting them.
Other folders that may be on your hard drive:
$NtServicePackUninstallIDNMitigationAPIs$
$NtServicePackUninstallNLSDownlevelMapping$
Created if and when you installed IE7.
If you delete them you will no longer be able to uninstall IE7
$NtServicePackUninstall$
Created when you install a service pack.
If you are currently using XP with SP2
then if you remove the folder you can no longer
uninstall SP2. When and if you install SP3 this folder will be
deleted and replaced by a new SP3 $NtServicePackUninstall$
folder to be used if you uninstall SP3.
If you have already installed SP3 then I would leave
this folder as is, at least until you are certain that no bugs have
cropped up after installing SP3.
Note: Once you delete this folder you are stuck with SP3
Warning: One folder you should not delete is: $hf_mig$
(and any folders that are part of/contained in $hf_mig$)
It is a necessary folder for future updates
Also See Doug Knox's page on this issue:
http://www.dougknox.com/xp/utils/xp_hotfix_backup.htm
And:
Is it safe to delete the $NtUninstallKBxxxxxx$ folders:
http://www.pagestart.com/ntuninstall.html