Who ever upgraded it' iPAD to version 4.2.1 using as most of us Window xp or windows 7 , please note that the all half Giga is stiill sitting there on the Desk top doing nothing.
The name of the file is iPad1,1_4.2.1_8C148_Restore.ipsw
In Windows XP it sits in C:\Documents and Settings\User\Application Data\Apple Computer\iTunes\iPad Software Updates
You can safely delete it since you are already working more then a month with it.
I didn't check for the location in Windows 7 that runs on my desk-top.
Hope some one will put it here as a follow up/