InstallutilLib.dll error

I just installed GIMP today and while I was installing it, I remember
seeing a message that it was changing the extention of a dll file and
that I might have difficulty running other programs. Well, I should
have paid attention. Now, when I'm trying to install software from
collages.net, this is what I get:

Error 1001.InstallutilLib.dll.unknown error.

I am your basic computer user, so please be VERY basic with me! Thanks!