I too was having this problem with BF2. I don't play AA so I can't comment on that. My system specs (for reference):
AMD Athlon 64 X2 4800+
2 XFX 7800 GTX in SLI
DFL lanparty UT SLI-DR mobo
4 GB PC 4800 OCZ Platinum memory
Audigy 4 Pro
2 500 GB SATA drives in a nVidia RAID 0
Antec 550 watt PSU
Obviously, I figured I could play the game with all settings maxed out, and I could for a day or so. Then I started having a crash to the desktop in single player and a hard freeze in multiplayer.
After reading this thread, and the threads linked here, I was able to fix the problem on my system. I write this to encourage anyone having these problems that it *can* be fixed, you just have to find out what is the specific issue on your system.
For me, the game works fine with all settings maxed if I do both of these things:
1. Disable my firewall software and antivirus software.
2. Set Audio rendering to software and medium quality.
If I just do one of the above, I keep crashing. Also, I don't have any lockups, freezes or crashes in any other game or application. I play CS:S, HL2, Doom 3, Far Cry, UT 2003 and 2004, Rome: Total War, Halo, MSFT Flight Sim 2004, Thief: Deadly Shadows, Dues EX: Invisible War and many other "heavy" games on my rig with no problems. BF2 is the only game that requires troubleshooting to run. I consider this a problem with BF2 and not with my system.
I hope this is helpful to someone.