Vista - Slow Performance, What Could/Should I Do?

When I first got Vista, everything worked perfect. But now, I can't even
watch a streaming video from the internet. I know it's not my internet
because my other Windows XP computer plays the videos just fine. (I also
can't play online games because I get booted all the time.)

Looking at my computers task manager performance tracker, my internet
utilization never goes above 10%. The CPU usage while playing the videos
also never goes above 10%. My first instinct is to question my memory.

So, task manager is telling me that I have a total of 2813MB of Physical
Memory, and 2229MB is Cached, which leaves 46MB free.

Is this a problem with my Cached Memory? Now, I know Cached Memory is good,
but how much becomes bad? I haven't found any Administrative Tools in Vista,
so where to I go to change that if need be?

Or am I looking in the wrong spot?

Thanks,
Grorange