Help with this error report

My imac keeps shutting down and giving me the following error report. Can someone tell me what I should do? Thx.

Interval Since Last Panic Report: 34681367 sec
Panics Since Last Report: 2
Anonymous UUID: AA876D83-9D81-4520-A1C2-6B497399CD7C

Mon Aug 29 13:33:02 2011
panic(cpu 0 caller 0x00044040): "zalloc: \"threads\" (294634 elements) retry fail 3"@/SourceCache/xnu/xnu-1228.15.4/osfmk/kern/zalloc.c:966
Latest stack backtrace for cpu 0:
Backtrace:
0x0009CC88 0x0009D63C 0x00029DA0 0x00044040 0x0003D034 0x0003D3F8 0x0003D490 0x00337D38
0x3E6B7CA0 0x3E6B8E8C 0x3E6B8F70 0x3E6AE554 0x3E6B60F8 0x3E6B857C 0x3E6B83EC 0x0003F2A0
0x000B1DD4
Kernel loadable modules in backtrace (with dependencies):
com.apple.iokit.IOATABlockStorage(2.0.6)@0x3e6ab000->0x3e6bdfff
dependency: com.apple.iokit.IOStorageFamily(1.5.6)@0x3e64e000
dependency: com.apple.iokit.IOATAFamily(2.0.1)@0x3db9c000
Proceeding back via exception chain:
Exception state (sv=0x356bea00)
PC=0x00000000; MSR=0x0000D030; DAR=0x00000000; DSISR=0x00000000; LR=0x00000000; R1=0x00000000; XCP=0x00000000 (Unknown)

BSD process name corresponding to current thread: kernel_task

Mac OS version:
9L31a

Kernel version:
Darwin Kernel Version 9.8.0: Wed Jul 15 16:57:01 PDT 2009; root:xnu-1228.15.4~1/RELEASE_PPC
System model name: PowerMac8,1

System uptime in nanoseconds: 77744930242486
vm objects:4055940
kernel map entries:2838528
kalloc.32:1773568
kalloc.64:2539520
vm pages:22498696
ipc ports:41818000
MAC Labels:1273284
threads:275777424
uthreads:122570240
vnodes:4871520
namecache:1676880
HFS node:7570976
HFS fork:2215696
buf.512:1740800
buf.4096:2514944
buf.8192:52404224
Kernel Stacks:2441216
Kalloc.Large:3895982
unloaded kexts:
com.apple.driver.iTunesPhoneDriver 1.0 - last unloaded 2272266341177
loaded kexts:
com.apple.driver.iTunesPhoneDriver 1.0 - last loaded 2270225720546
com.apple.filesystems.msdosfs 1.5.5
com.apple.filesystems.autofs 2.0.2
com.apple.driver.AppleOnyxAudio 2.5.8f1
com.apple.iokit.IOBluetoothSerialManager 2.1.9f10
com.apple.driver.DiskImages 199
com.apple.driver.MotorolaSM56K 1.3.9
com.apple.GeForcePPC 5.4.8
com.apple.driver.AudioIPCDriver 1.0.6
com.apple.driver.IOBluetoothHIDDriver 2.1.9f10
com.apple.driver.AppleHWSensor 1.9d0
com.apple.iokit.AppleGMACEthernet 1.5.9f1
com.apple.driver.AirPortBrcm43xx 367.91.22
com.apple.iokit.IOFireWireIP 1.7.7
com.apple.driver.SMU_Neo2_PlatformPlugin 3.4.0d0
com.apple.driver.AppleSMUMonitor 1.9d0
com.apple.AppleOnboardDisplay 1.15.1
com.apple.driver.AppleI2S 1.0.1f1
com.apple.driver.AppleLM7x 1.9d0
com.apple.nvidia.nv30hal 5.4.8
com.apple.driver.AppleK2Driver 1.7.2f1
com.apple.driver.CSRUSBBluetoothHCIController 2.1.9f10
com.apple.driver.AppleUSBMergeNub 3.5.2
com.apple.driver.ApplePulsar 1.5.2d0
com.apple.iokit.IOUSBMassStorageClass 2.0.8
com.apple.driver.XsanFilter 2.7.91
com.apple.iokit.IOSCSIMultimediaCommandsDevice 2.1.1
com.apple.iokit.SCSITaskUserClient 2.1.1
com.apple.iokit.IOATABlockStorage 2.0.6
com.apple.driver.AppleUSBHub 3.4.9
com.apple.iokit.IOUSBUserClient 3.5.2
com.apple.iokit.IOATAPIProtocolTransport 1.5.3
com.apple.driver.AppleK2S@