From microsoft

[tlarson1]

Does this mean I've reinstalled this so many times for nothing?
"SP1 eliminates the need to reinstall the service pack after installing new system components or devices."

 

[Shadow07]

Yes. When you install the service pack, it will copy over the i386 folder on the service pack CD to a folder in the %SYSTEMROOT%\Service Pack Files\i386. It should also make a registry setting change in the HKLM\Software\Microsoft\Windows\CurrentVersion\Setup. The key you would look for is a REG_Z key called ServicePackSourcePath that would have the value of the path I stated above. Every service pack will install in this path. But, I have come across some machines that do not have the registry entry that I mentioned above. You should check to make sure.

And, you will never need to manually install the service pack again, like before in the Windows NT 4 days.