I've noticed some web pages are accessed by associating numbers next to the 'www' part of the url. For example:

http://www38.wolframalpha.com/input/?i=1%2B1

What does this mean? How would I be able to configure that for some of my own sites? Is it DNS side?

Thanks

This is really quite simple
the www. prefix is irelevant to your site I.E. daniweb.com and www.daniweb.com go to the same server but www. can be treated as a subdomain for example
daniweb.com could go to server1 (IP 123.123.123.0)
BUT!
www.daniweb.com could go to server2 (IP 123.123.123.1)
so
www2.daniweb.com could go to a third server. This method can be used to distribute load among many servers but I don't think this is the best method. I would always use Apache with ether mod_backhand or some other configuration of mod_p-r-o-x-y (Take out the dashes, for some reason my school blocks that word)
So in answer to your question this is a DNS setting but it is not recomended
Regards,
Sam Rudge

Thanks for the explanation, i get it now :)