Casey613 wrote:
It's not possible unless you use a third-party software which is illegal
Not exactly. It is possible to run 2 or more clients at the same time on the same computer legally. For example, VMware. (There is already a topic around here somewhere about running more than one client - not multiclient).
Third party software is not illegal. Third party software that is used to modify the SRO client
is illegal. If you claim that running SRO through something like VMware is illegal, then it must be illegal to run AOL Instant messenger, or Ventrillo, or Teamspeak, or Microsoft Word, etc., while running SRO.
You can certainly install VMware server on your system, and have it run multiple operating systems, with one copy of SRO running on each operating system. That is definitely not illegal. No more illegal than having two computers on your home network running SRO.
VMware is a LOT of overhead just to run multiple SROs, but it is possible to do.
There may be other ways as well.
Edit: I jumped the gun a bit. Others above have mentioned virtual PC tools like VMware and Virtual PC. Still, that's overkill just to run multiple clients. Linux might be able to do it without emulating an entire OS... if I still had Linux installed, I'd test it.