Hi,
I have a site with the following stats:
773 859 visitors month
2 126 395 page views month
220 average users online (picking 450)
493564 comments
128709 news items
10186 registered users
I'm running it on a dedicated server:
Cpu: Core 2 Quad 2.83 GHz
Memory: 2048 MB
I'm hosting it in surpasshosting.com and pay 250$ month
Even when running in a dedicated server you will have to pay attention to your queries, check out which ones are more time consuming and try to optimize them.
Ex: If you are having a lot of comments in the news items you should add a key to com_rootid in comments table.
Use cache for blocks whenever possible.
Monitor your server using this free program:
http://himonitor.com/Keep tables size small, do not log pageviews for example.
If you using a xoops stats module, uninstall it.
Delete protector last entries frequently, use cron job if needed.