If you’ve written more than a very simple BlackBerry application, you’ll know that you need to sign most applications with keys obtained from RIM. Getting keys from RIM and signing applications within Eclipse is an easy process and well documented on the BlackBerry web site.
If however you change computers, its a bit more difficult.  Depending on what you read you’ll see that the signing keys are tied to a single computer, or you need to request new keys from RIM, or you can just copy keys between computers.
The latter of these is the closest to the truth, but there is still a sting in the tail.
When you move development computers, to move the code signing keys with you, you need to copy the following directory to the new computer.
Once you’ve copied the keys over, you need to import them into Eclipse using the “Import Existing Keys” option on the “Window | Preferences” dialog as shown below.
That appears to be everything you need to do, however if you try to sign some code now, you will get an error back:
The private key is not located in the sigtool.csk file
To overcome this issue, you need to copy the sigtool.csk and sigtool.db files that were copied above into the vmTools folder.
Having followed these steps, you should be able to sign applications on a new computer.