Restoring default XP SP2 registry keys

I was not able to install a new version of an engineering software package
because something was left behind in the registry from the older version that
I had removed. So I stupidly deleted a couple of registry keys that looked
related to the software without documenting them (not just the tags, but the
folders with the long alphanumeric strings). Now when I try to install the
software it gives me an error. I ran system restore but the problem is still
there (I don't think it restored the registry keys I deleted). Is there a
way to install all of the default Windows SP2 registry keys or to download
and reinstall SP2 in general?

Thanks!