Try right clicking Combat Arms > Properties > Compatibility Tab > Under "Compatibility Mode" check the box that says "Run this program in compatibility mode for:" > Select either Windows 2000 or Windows XP (Service Pack 2) > Click Apply, and presto.
If that doesn't work, a reinstall is always a possibility.
(I use Windows 2000, never had problems with it. You can always change it later. I'm running Windows Vista, recently bought my laptop, 3GB ram, etc.)
Turn off your AIM/MSN/Yahoo/Xfire/etc off.
It helps.
Close everything you don't need pretty much, webcam/microphone/bluetooth, etc.
Little things still help
Also, increasing your virtual memory may help.
Right click My Computer > Properties
(For Vista: Right click Computer, then click "Advanced System Settings")
Now you should have a System Properties window open,
click the Advanced tab,
Under Performance, click the Settings box.
A window called Performance Options should've popped up.
Look for Virtual Memory, and after "Total paging file size for all drives: (Number here)
Remember that number, and click the Change box.
A window called Virtual Memory will come up.
Click the "Custom size:" option.
Initial size (MB) and Maximum size (MB) should have a box after them with a number in it.
The rule for this number is 1.5 times the amount of ram you have.
Ex: If you have 3GB of ram, you may put 4500.
If you listened and remember the number I told you to (You can always take a few steps back and get it again.)
you may enter that, or the amount of ram you have, times 1.5
It may be less than 1.5 times, but it's the recommended amount.
Hopefully I help, if you have questions, just send me a PM.
(Yes, I've done this to my computer.) You probably can find a video on YouTube if you don't believe me.
Also, doing a weekly scan helps, I suggest downloading CCleaner (For more information on CCleaner, here's the link for it on WikiPedia.
http://en.wikipedia.org/wiki/Ccleaner ) it's somewhat like the default Disk Cleanup, but is quite better.
Also has a registry cleaner.
I use CCleaner about everyday, and haven't had problems with it since.
Turning down your settings in Combat Arms also may help, so what if your graphics aren't as clear, at least you can play with less lag, right?
For further questions/more information, please visit
http://www.combatarmsforums.com/showthread.php?t=276