One of my test machines that is still running Windows XP just HUNG while performing Windows Update Today.
At the "Checking for latest updates" page it just kept checking and checking and checking.......
It turns out that it was some bad files. Maybe a prior failed dowload or something.
Here are the steps I used to solve the problem.
Click On Start --> Run
Enter Cmd and hit return.
At the command prompt and type 'proxycfg -d' (This will clear the proxy cache, don't worry if it complains about there not being a proxy.)
Type 'net stop wuauserv' to stop the automatic updates service. (You must do this and it must succeed in stopping the service or your won't be able to do the next step.)
Delete all the contents of C:\WINDOWS\SoftwareDistribution.
Go back to the command prompt and type 'net start wuauserv' to restart the automatic updates.
Run Windows update again.