should automatically detect proxy server be disabled & is cacheman 5 still useful for winxp?

[RayEarth]

awhile back my modem had problems with connections and so the isp sent a tech to check my cable and he said that because I had the "automatically detect proxy server" setting on, it causes problems, but that's on by default in IE and I never had a problem with it for the over 2 years, I think the tech just said anything just to make it look like he did something before leaving. So should I leave detect proxy server setting on, use web browser setting or just disable it? and is there a need for cacheman 5 in winxp or is winxp already optimized?