I'm a member of a large gaming community that is currently split among three different sites. We are now gaining sponsors and need to consolidate our presence to one site. I'm the head of the team that will design the change and implement it.

After looking at all the major CMSs and forum software packages, we have chosen vBulletin as the system to build the new community site around. Interestingly enough, DaniWeb is what convinced my "bosses" in the clan that vBulletin is more than capable to handle the type of load we currently have while being more than capable to expand in the future.

So, now for my question. I'm having a hard time finding reliable information about what kind of hardware is required to support vBulletin installations that run at specific activity loads. For example, we have more than 4000 unique registered members across the three sites currently and average anywhere from 100-200 concurrently active users at any one time. Are there any basic hardware specs for the server that anyone here can recommend that will ensure that the site remains quick and responsive?

If I may be so bold, I'd like to hear a recommendation from Dani since she has definitely succeeded in creating a very responsive site running a very large number of concurrent users.