I think the PHP error is a red herring. That error has been turning up in my PHP logs for months it seems and the CMS has been running fine. This morning I disabled zip from loading and although the PHP error went away, the CMS is still failing to load.
Regarding Apache, I find this in the error logs:
[Tue Jun 08 09:21:49 2010] [error] [client 158.166.236.29] File does not exist: C:/wamp/www/[my path]/SilverStripe/OlafIntranet, referer: http://dev-intranet/Security/login?BackURL=%2Fadmin%2F
[Tue Jun 08 09:21:49 2010] [error] [client 158.166.236.29] File does not exist: C:/wamp/www/[my path]/SilverStripe/OlafIntranet, referer: http://dev-intranet/Security/login?BackURL=%2Fadmin%2F
[Tue Jun 08 09:21:49 2010] [error] [client 158.166.236.29] File does not exist: C:/wamp/www/[my path]/SilverStripe/OlafIntranet, referer: http://dev-intranet/Security/login?BackURL=%2Fadmin%2F
[Tue Jun 08 09:21:49 2010] [error] [client 158.166.236.29] File does not exist: C:/wamp/www/[my path]/SilverStripe/OlafIntranet, referer: http://dev-intranet/Security/login?BackURL=%2Fadmin%2F
And CMS still not loading...