www issue over wp install

I’ve installed WP 40+ times successfully. Each time I’ve added in www to both applicable url fields, and then reloggedin, created site etc.

However having done several 2.7.1 installs this morning (on 2 different hosts, one using fantastico, the other simple scripts) this doesnt wrk. I get the apache / cp installed page when accessing my home page – but other links to pages posts work.

If I revert to taking out the www it works again. I can live with this by using a canonical plugin, but am worried that I perhaps shoudnt have done this on my other sites?

Any advice / pointers, very gratefully received.