I'm not a noob but it seems like such a basic question that I thought this would be the best place. Mods please move if necessary.
I own several sites. On one of them I wish to setup a blog and for mysite.com/blog/ to be on a different server at a different hosting company. Visitors would still see mysite.com/blog/post-url.htm in their browser but the whole blog would reside elsewhere. And visitors can still browse mysite.com/any-other-page.htm at the current host.
I know how to setup a 301 in htaccess but, obviously, that's not what I'm looking for here. Any advice?
OK, if you go for the subdomain, then once you have set up the external hosting (as a virtual host or whatever) you simply need to add a new entry in your DNS record for the primary domain which directs traffic requesting the subdomain to the appropriate server.
You have the choice of using an A record or a CNAME: for the A record, you specify the IP address of the subdomain's server:
blog 10800 IN A 188.8.131.52
This is fine if you have a dedicated IP for the subdomain or you are sure the IP address will not change without you being notified well in advance.
The other option, which is not dependent on a particular IP address for the subdomain (thus making the solution more robust than an A record), is to use a CNAME to another subdomain defined for the resource. For example, many hosting companies have an option to access a site via a subdomain of their own domain. You can delegate the DNS to that name:
blog 10800 IN CNAME oddsodsblog.myhostingco.tld.
If finally you decide to go for a subdirectory and not a subdomain, you have to set up a reverse proxy on your primary server to allow requests for the /blog/ subdirectory to be handled by the different server.