As mentioned they are the uninstall info for service packs and hot fixes. I keep them for about a month and then delete them.
If you want to remove the entries from add remove programs also try this.
Clear Unwanted Entries from Add/Remove Programs
Intended For
Windows XP
Windows 2000
Windows Me
Windows 98
Windows 95
In Add/Remove Programs in Control Panel,
a list of installed applications is displayed for the purpose of easy removal.
Unfortunately, but there is no obvious method for removing these entries
(either to prevent accidental removal, or if the application was removed some other way)
without uninstalling the programs. To remove an entry, do the following:
Run the Registry Editor (REGEDIT.EXE).
Open HKEY_LOCAL_MACHINE\ SOFTWARE\ Microsoft\ Windows\ CurrentVersion\ Uninstall,
and remove any unwanted keys under "Uninstall."