Well, first up, RAM is not universal, there are many different varieties. This is why the memory configurator that crucial.com has can be useful, sometimes you have no clue what will fit where, and all the various different types.
Generally, for taskmanager I google the various processes to figure out what they do.
This is a good place to start
http://www.answersthatwork.com/Taskl...s/tasklist.htm .
Some of the more normal stuff I have running is (win2k sp4)
System idle Process
System
winlogon.exe
svchost.exe
spoolsv.exe
services.exe
among others that might be more specific to the system depending on running programs.
Sudden slow downs can be caused by
scheduled tasks (virus scan/defrag, etc)
spyware (run spybot/adaware/etc)
hard drive issues (full/needs a defrag/bad sectors [run scandisk]/etc)
could also be some security software or something loading in the startup (I like this program to look at what's in my startup
http://www.mlin.net/StartupCPL.shtml )
Hope that some of this is useful to you.