problems with tf2, help?

I have a dual core 2.6ghz, 4gig ram, 512mb 8 series graphics card pc with windows vista and I can't play this game!I'm at wits end, I don't know what to do! What happens is i'll be playing the game just fine, when randomly, I seem to run into a random lag spike. Everyone else keeps moving, and my screen just jostles around. Sometimes, when this happens, a corpse will drop below everyone on my screen, whether or not they are dead. (ie, if they're still alive, they'll be standing on top of said corpse) It also cycles through the weapons like it does when you respawn. Any help whatsoever as to what could possibly be causing this would be greatly appreciated. I have a DSL internet connection and can run any other game just fine. Is this possibly a vista problem? Or is my pc just fubar'd. *sigh* When i'm not experiencing these random spikes, I love the game. In it's current state though, it is not playable.Thanksproblems with tf2, help?
Here is a better description of what is happening to me. Exact same thing. (I also Dl'd it from steam.)http://hardware.gotfrag.com/portal/forums/thread/312067/problems with tf2, help?
I think you should just defrag, because the source engine has its stuff all cached.
>_>.... sorry. double post.
it's a brand new pc. Defrag? Nope, dont need to.
It's definitely not a vista problem... o_o
Could your Firewall or Antivirus be the problem? Some of these can interfere with Steam games.
does vista have it's own firewall? I disabled my norton firewall %26 antivirus.