P.S.S.
In case Service Pack has been applied:
If you have applied Service Pack 2, then consider some more cleanups.
See Aumha page on "Tidying up after installing SP2"
http://forum.aumha.org/viewtopic.php?t=7265
Substantial space can be reclaimed after having installed a Service Pack --- you can archive (to CDs) or remove the SP "un-install" set of data.
If you are really double-sure positive you'd never want to undo old patches --
then you could delete the individual $NtUninstallQnnnnnn folders (located in folder \Windows or \WINNT ).
Just know that would make the old patches un-installable .
Those are individual hotfix un-install folders. You may delete those.
The registry will have leftover entries; so you may want to get into Add/Remove Programs,
select these items. It will fail the uninstall, and then allow you to remove listing from registry.
Also, be aware, if you made recent 'optional' updates 'after' installing service pack ---
then those would be among that set of folders.
If you will never need to un-install SP2, the $NTServicePackUninstall$ folder can be removed.