Still no luck :( I can't see it in the list. Also I can't see that "#label" in other PRWidget subclasses.
Ok, I have a "file out" of my package with just one PRWidget subclass:

PRWidget subclass: #PMKHeaderWidget
    instanceVariableNames: ''
    classVariableNames: ''
    poolDictionaries: ''
    category: 'Pier-My-Widgets'!

!PMKHeaderWidget methodsFor: 'rendering' stamp: 'kmz 5/29/2007 03:19'!
renderContentOn: html
    html header: 'yoyo'.
! !


!PMKHeaderWidget methodsFor: 'initialization' stamp: 'kmz 5/29/2007 02:52'!
initialize
    super initialize.! !


!PMKHeaderWidget methodsFor: 'accessing' stamp: 'kmz 5/29/2007 03:04'!
asLabel
    ^ 'KmzHeader'! !

!PMKHeaderWidget methodsFor: 'accessing' stamp: 'kmz 5/29/2007 03:16'!
defaultCssClass
    ^ 'box'! !

!PMKHeaderWidget methodsFor: 'accessing' stamp: 'kmz 5/29/2007 03:16'!
isAbstract
    ^ false! !

!PMKHeaderWidget methodsFor: 'accessing' stamp: 'kmz 5/29/2007 03:04'!
label
    ^ 'KmzHeader'! !

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I have an image running with this package on: http://kamikaze.seasidehosting.st  (editale, feel free to break all :))