I read that after Win XP SP1 installation is OK, to save space the archive folder c:\windows\ServicePackFiles can be deleted for saving space. However, I noticed in the Windows folder a whole bunch of other folders that came as a result of installing other fixes and patches as follows: $NtServicePackUninstall$ $NtUninstallKB810217$ $NtUninstallKB817778$ $NtUninstallKB820291$ $NtUninstallKB821253$ + 9 more like these, then $NtUninstallQ322011$ $NtUninstallQ327979$ + 3 more like these $xpsp1hfm$ Can these folders also be deleted assuming everything is running OK?

Yes, they can, these are the uninstall folders for various Windows Updates. Be aware that if you delete these, you cannot uninstall any of these Windows Updates that might prove to be problematic later!

In addition to the above, you'll see those in your add/remove programs. If you delete the backups, you can then remove them from the list by selecting them in add/remove and it will tell you the files are gone and prompt you to remove them from the list.