To speed up Halo:
1. After you have started your game, hit ctr + alt + del. Or alt + tab and open your Task Manager [right click on bar conntected to start].
2. Click the processes tab.

3. Find the program (halo.exe) under Image Name. This may be easier to find if you order the list by User Name.

4. Right click the process, choose Set Priority, and choose above normal.

And you're done! Your gameplay should now be much smoother.
What else can I do with task managing/prioritizing?
This is probably one of the best ways to keep your computer going fast, always go to your processes tab to see what's REALLY running on your computer. Many programs are invisible, including viruses and spyware. You shouldn't mess with things under Local Service, Network Service, or System unless you really know what you are doing. However, if you see programs under your Username that look suspicious, go ahead and end them all and see what it does. Make sure any work has been saved first though. As for priorities, raising a priority higher then the rest means, I want to make sure this program is going faster then the others, or lowering it does the opposite. Hope I didn't bore you all to death! - Sconer