Please provide some details of what you've encountered that's gone wrong with the upgrade, such as any diagnostics or error messages received, any revelent output from a verbose bootstrap, and some information on what OS X version you're looking to upgrade to.
i have tried upgrading to mac ox 10.6.5/6/7/8 or even combo updates. but when i try to upgrade to 10.6.4 it says some error and the upgrade doesn't start but while with the other upgrades the upgradation starts but after i restart my mac book the apple grey screen comes up and it hangs with the spinning wheel. i have done fresh installs of mac os x 10.6.3 so many times. the machine is bootable only in 10.6.3 i cant even boot the machine into safe mode or even diagnostics after the upgrade as it hangs . when my macbook pro is working fine with the fresh install of mac os x 10.6.3 the S-ATA column in the system profiler says unknown AHCI standard controller.
You've tried upgrading. Multiple times. You've tried an upgrade to 10.6.4. That failed. You've tried the combo update. That failed. You've restarted the processing by reinstalling 10.6.3, and that's worked. You want to upgrade to 10.6.8. You've repeated this sequence. You've made this part of the problem quite clear.
Unfortunately, there are many potential triggers.
If you have not already repeated the download, re-download the 10.6.8 Combo upgrade kit from Apple.
I'll presume you have sufficient free storage space on the device to allow the upgrade. If not, then offload some of your larger files to external storage, or delete any user-loaded files that you no longer require.
Before commencing the next "upgradation" upgrade sequence, disconnect all external devices. Disconnect all USB devices. This includes any external keyboard, external mouse, and external storage devices. Use only the Apple-integrated hardware for your particular model of MacBook Pro.
Now for the most important part of troubleshooting this: what is the exact wording, and the specific messages, and the actual output that is produced when the upgrade fails. The specific wording of these unspecified diagnostics, and the last dozen or two commands and related output of the last section of the verbose output prior to whatever happens - matters.
If you're not in a position to provide the specific wording or diagnostics or related - and consider photographing the error dialog boxes rather than copying those down, for instance - then you're going to want to visit with the local Apple store or contact Apple or your local Apple reseller directly.
I don't see any errors in that.
The next piece after DSMOS gets done is usually a hunk of the network startup. That's apparently either failing here, or it's really, really, unusually, really slow.
In addition to having everything USB and FireWire disconnected, and the new Combo kit download, the other brute-force approach involves using Disk Utility while booted from the DVD to perform a repair permissions and (while you're at it) a repair volume.
There's also a potentially-related discussion here. That's got some differences, but the failure is in a similar spot.
If you have a locall Apple store or Apple reseller, it'd be worth a chat with them, too.
mr hoffman i will try to do what u said but 1 more thing i want to tell u is that i have 8GB(2 X 4 GB) 1333 MHz DDR3 Ram installed. if the system is working fine with those RAM's with the fresh install of MAC OS X 10.6.3 then i think it shouldnt have any problem in upgrading too. isn't it? let me remind you i have a macbook pro 13 mid 2010 which originally is shipped with 2 x2 GB 1066 MHz DDR3 RAM.