There are many solutions and I'm going to post each of mine that works.
Things you should know...
I have a Windows 7, 64 Bit, Intel Pentium 4 HT 3.2 GHz with 2 GB of ram and I can run APB Fine.
SOLUTION #1 : VIRTUAL RAM
Go to Start -> Right ClickMy Computer -> Properties -> Advanced System Settings -> Advanced Tab -> Performance Settings.
Select Adjust for Best Performance. Go to the Advanced Tab and Under Virtual Memory select Change. Select Custom Size and adjust the setting according to the size of your current available hard drive space that you want for Virtual Memory. Currently I have mine set to 10000 - 10000. Once finished select Set and you should be prompted to Restart. Even if you aren't RESTART.
Right clickAPB.exe -> Send to -> Desktop (create shortcut) . ALWAYS USE THIS SHORTCUT. Bucket 1 is minimal so in-game press O -> Video Settings and set it to Minimal. Then select the Advanced tab and make sure everything is off and at the lowest possible setting. Every 2 weeks or if you get a file error make a backup of the APBCombat.ini and run the loader to update, then replace the APBCombat.ini again.
If you liked my Guide and it worked, thank me.
Credits and props go out to Google.
If it didn't work for you, too bad, thank me anyways.
Oh and if your reading this as a Moderator, sticky.
I think you run it fine because of your CPU, I have 8 GB RAM but a 1.9 ghz CPU (I'm on a laptop) so that makes it worse and my graphics card, but i still seems to do good with 30-50 fps not doing anything 20-30 fps driving and 30 to 20 are lower in combat On a different note. Some people just suck A lot..