BleepingComputer.com: Performance has taken a dive

About three weeks ago, my computer rather suddenly lost its spunk. I use it for both gaming and school work (with the former taking sudden precedence as I have graduated and entered the world of joblessness). It was a moderately powerful system, handling most programs thrown at it with barely a hiccup. Now it struggles with programs for which it far exceeds the minimum specs, and any game released in the last three years is out of the question. It even gasps for breath when I visit script-intensive websites in Firefox or try to play high-definition videos from the internet. Several Flash applications that used to run fine will choke up my system.

I've done all the obvious things to see if I can squeeze out all the performance I can get - I've scanned with AdAware, AVG8 for viruses, A-squared for trojans. I downloaded the TweakGuide Total Codex (user-friendly guide to working with Windows) and followed much of the advice within, I downloaded the program Autoruns to stop most of the auto-starting programs from auto-starting (leaving only what seemed to be necessary for Windows and hardware running). I even uninstalled and updated my video driver. The one obvious thing I haven't done is update Windows, because the Windows automatic updater was the cause of constant crashing a few months ago. But until I hear of some horrible bug in Windows that causes it to devour system hardware from within after exactly 17 months of running, I'd like to stay away from that avenue altogether.

I'd love to be able to figure out what's eating my system. Any diagnostic tricks or suggestions that just might work would be welcome.

My system specs are:

Toshiba Satellite X205
Intel® Core™2 Duo CPU T5450 @ 1.66GHz
2GB RAM
NVIDIA GeForce 8700M GT
7200rpm HDD 250gb, 2 partitions
Windows Vista Home Premium 32-bit

Your help is appreciated!

hello hostis
have you tried the memory test within windows?
start>all programs>administrative tools>mem test.
also defrag dont hurt

let us know

Memory diagnostics tool found zilch. And defrag is set to go once a week, it was defragged last Wednesday.

howabout ccleaner (DO NOT USE REGISTER CLEANING PART)delete temp files and such.
http://www.ccleaner.com/download

maybe system restore?
did you install sp2?

Sure, I've deleted all the temp files. System restore isn't an option at this point (i've been fudging with this for too long). I haven't heard anything about SP2 that suggests it might fix my problem, and I'm reluctant to install it until I see evidence to the contrary. My computer worked just fine for a year and a half without SP2, so it should still work fine without it. I might be convinced to, but I'd like to see what else there is to try first.

one more thing i can think of . go to task manager>performance tab. what does the little memory window say ie 1.34 GB (thats what mine shows) and i have 3 GB installed.
just thought id throw one more idea.
good luck