I have started to run into problems becuae some users use www.domain.com and some hit it as just domain.com
When the forum sends out email it was sending it under domain.com always.  If the user clicked on the email link back to the forum they come back as domain.com always even if they were browsing under www.domain.com.  Their stored cookies for login are under the www address and so they aren't logged in.
I had two portal alias's, one to domain.com and one to www.domain.com, in that order.  I assume the forum module was using the first domain alias.

So, I would like to get everyone on www consistantly so they all get links that work.  I moved the www.domain.com alias to the first position and now the forum sends links using www.  So far so good.  But any user using just domain.com will now have the reverse issue.

Is there a way to have the sevrer always respond with the full www.domain.com no matter what the user originally types in so that all links to my site will be consistant?

This is a common problem, and isn't just an annoyance, it can affect your site rankings in search engines as they will detect the two different versions of the domain as duplicate content and you won't rank as well as you should.

One option for you to use is the Url Master module that I distribute : this has a 'redirect to chosen subdomain' field in it.  To set up an automatic 301 redirect from the non-www to www version, you just tick this box and type in 'www'.  You can get a trial download version here : Url Master Trial Download