Hi,
If my forum were to have separate topics as;
Topic 1
Topic 2
Topic 3 ... etc
would there be a way for these to have their own subdomains eg topic1.mydomain.com?
You would have to fix rip apart a lot of SMF's code, and configure your webserver properly, but yes, it's 'possible' with enough programming time.
Take a look at http://custom.simplemachines.org/mods/index.php?mod=636
It changes your links as they were subfolders.