I doubt seriously whether anywhere in the world you could lawfully watch Star Trek: Enterprise online. According to MA, it is, however, telecast on Australian Sci-Fi, weekdays at 6:30pm and 11:30pm, Saturday and Monday at 10:30pm. I imagine your question specifies "online" because although you have broadband internet, you don't have access to Australian Sci-Fi.
We have a similar problem in the U.S., where neither Star Trek: Deep Space Nine nor Star Trek: Voyager currently air on American television. I imagine our Sci Fi Channel, now called "SyFy", is getting numerous emailed requests, but so far they're not cooperating. Thus, we feel your pain ProfessorTrek 05:30, August 6, 2011 (UTC)
Who said something about "lawfully"? Try www.allstepisodes.com, you can watch all Star Trek series there.
If you have a streaming service like Netflix, you can watch it.