How do I revert my iPod touch 8 GB (2nd Generation) to ios 3.2?
As bckbck already said, you need the SHSH blob from the earlier version. If you don't have it for the desired OS version, it's too late.

And iOS 3.2 was only supported on the iPad, so it won't run on iPod touches.

Should the data on http://theiphonewiki.com/wiki/index.php?title=SHSH be correct, then you can downgrade to iOS 4.1 with your device.

And you can get all firmwares at http://www.felixbruns.de/iPod/firmware/.