Memory usage on Red Hat

[ubergoonz]

I have a RHEL server that hugs for no particular reason .. so I need to do 
some performance monitoring.
 I am trying to understand how memory are being used and used by what 
process on Linux. 
comming from Solaris background, I am more familiar on tools available on 
Solaris.
 I wonder if anyone can point me to articles to readup on what's shared, 
buffers, cached memory are being used in RHEL fromt he `free, vmstat` 
outputs.
 and what are equiv to truss, pstack, ptree on Linux if there are similiar 
tools around.

-- 
Best Regards,
Leslie Joshua Wang