Establish a performance baseline for terminal server windows machines

performance-monitoringperformance-tuningwindows-terminal-services

I need to establish a performace basline for our Terminal Server machines.

i plan to use perfmon , and will have a SCOM server on the site very soon.

The terminals are used as a desktop environment for thin clients.
The users use office, outlook, IE8 for intranet apps (sharepoint portal internal sites)
and a .NET 2.0/3.5 enterprise data driven app.

some of the the servers are virtual hosted by Win2008 hypervisor, some are physical.
all are Windows 2003 SP2 32bit. all are on a SAN storage.

what counters should i gather ?
whats the sample interval ?
leave it always running , or have it run for a a sepcified period?
where can i find what are the acceptable ranges for the counters gatherd?

thanks in advance