You're still getting that error message even adding the trailing slash? Basically, the webserver/browser needs to do an extra lookup if you provide the URL without that slash, and I've found that it sometimes breaks IE. Do you get the same sort of error using a different browser like Netscape? Finally, and this will sound stupid so accept my apologies in advance, is Apache started? You can look in your hosts and lmhosts files (probably in c:\windows\system\drivers\etc) to make sure that a localhost entry does exist, but localhost is usually added by default so I doubt that's your problem. HTH.
geoff