Why does my game not use inactive memory

Question

MacBook Pro
15-inch, Late 2008
Processor  2.53 GHz Intel Core 2 Duo
Memory  4 GB 1067 MHz DDR3
Graphics  NVIDIA GeForce 9400M 256 MB
Lion 10.7.2
Here is my activity monitor: http://imgur.com/65ca9
What i'm running:
TF2 (hl2_osx)
Steam
When i'm playing Team Forchrease 2 I get about 80 to 100 Frams/sec(FPS), but the problem is every few seconds it dips down to 10~20 FPS which makes it very jittery. 
I noticed that while the game is running there is almost no free memory but there is 1GB of ram tied up in "inactive memory" which I thought would be used by anything that needed it.  Now i'm not sure if the game has enough ram and something else is cassing the problem... but I think i have a 1/2 decent graphics card and set up and I don't think I should have this much problems running at the lowest graphics seatting.
Any insight to this problem of the low FPS and why TF2 only uses 1 GB of memory that would be a great help!  Thanks
PS
I saw this guy: https://discussions.apple.com/message/16277771#16277771 but restarting my computer does not resolve this issue.
Message was edited by: Frankda4

Answer 1

Hi Frank,
Frankda4 wrote:
MacBook Pro
15-inch, Late 2008
Processor  2.53 GHz Intel Core 2 Duo
Memory  4 GB 1067 MHz DDR3
Graphics  NVIDIA GeForce 9400M 256 MB
Lion 10.7.2
there is 1GB of ram tied up in "inactive memory" which I thought would be used by anything that needed it.
Not video. You have 256MB VRAM for video, which is rather low for today's video needs. I believe that is the issue.