Well thanks so much, now I get the login page.
Sitebuilder web site was in fact using plesk default app pool, I just created an independent pool and attached the website to that new pool, and that was enuff to make it work, I didin't have to do the rest.
Finally, my only problem left is that i'm trying to log in with user and pwd:
admin, sitebuilder
admin, admin
root, sitebuilder
root, root
and I can't login, I get:
Error: The supplied credentials are invalid, what's the defaulkt user name and pwd for sitebuilder 3.2 for windows?