rofl
uhmm the number of clients depends upon your proc and ofc most important the RAM you have
for eg. If u have Win7 and total RAM 4Go. Win 7 takes about 800Mo. So u are left with 3.2Go
if Win 7 (32bit) u loose 1go), so u are left with like 2.2Go, so u'll run like 4 clients. above it will close all
if Win7 (64 bit), u have the 3.2Go, so easy 6 clients
its always nicer to have 2 computers. Main PC Win 7 (64 bit) --3-4 Go RAM. so u can run 2 clients + xfire + skype + blabla
and on second computer WinXp with 3Go RAM max, u can run like 6 clients easy
the reason ur clients close == windows closes them due do memory being unsufficient on 99.9% cases
now last test i made was 19 clients running xd with skype and torrents on download

there a secret too, a file in Archlord if u delete it, ur game clients runs with 400Mo instead of 800Mo for eg