Mac OS X: Something is eating RAM memory in Snow Leopard

Something is eating RAM memory in Snow Leopard

"You can test if the problem is account specific by creating a new temporary user account to run for a while, and see if the problems persist there. If not, then the problem is more than likely in your old account's Library folder. Additionally, you can turn off third-party kernel extensions by booting into Safe Mode (hold shift at start-up), which will test for problems with extensions."
(from http://reviews.cnet.com/8301-13727_7-10351787-263.html)
So, the problem is possibly in my "old" account's Library folder. But then, when I start up in Safe Mode and log in to the "old" account, the problem is still there. Looking at Active Processes in Activity Monitor (still in Safe Mode) the process that takes up the most (and then more and more) Real Mem is kernel_task.
I'm definitely lost.
How did starting up in Safe Mode "test for problems with extensions" and how do I proceed to find the problem and then fix it?
I depend on the system plus the 2 apps I run all the time using exactly, or preferably less than, 50% of RAM so I can "quickly" (ahem, a relative term) fire up VMware Fusion and Windows off of BootCamp when necessary. My MacBook is the original kind and can only take max the 2G RAM I've got.