I just attempted to run multiple Second Life viewers on the old machine, and while it was possible, I noticed two issues at hand : the system ran out of virtual memory within the first 10 minutes of operation, and CPU temperature went through the roof. While it normally sits in the low to mid 50's, it was now pushed up to 65 degrees Celsius, which can't be healthy for the machine.
I'll do another test on the new(er) DuoCore machine and will possibly start using that one as a dedicated Second Life machine. That one also has 1GB of RAM if I'm not mistaken, which would definitely make things faster as well. Off to switch machines and see what happens.
Hm, I just remember that I don't have a spare set of speakers for that machine. May pick one up later today if the results are good.
Update : Initial tests are good. The 1GB of RAM and a less ancient processor definitely help running multiple clients - I tested for up to three - at once. I also tried out the WindLight viewer, but was not all that impressed with it's performance. Land that was otherwise very smooth now appeared jagged and edged to me. And I'm not imagining it, as I do happen to know my own sim rather well. The skies were fabulous though, that I'll give you.