Go for it. But if you try to do an upgrade it might stop you. But it won't hurt to try. A repair installation would get past the service pack thing. And and upgrade might let you do it. I'm not certain.
blah, blah, blah...the answer is YES!
The only problem is that if your i386 folder is corrupted at all you could screw yourself. Do you have an i386 folder on your CD? If so, copy it to the i386 folder that you already have. It will ask you if you want to replace, click YES TO ALL. This way you have a clean copy of all the files before doing an upgrade from the i386 folder.
Did I explain that clearly?