The Winamp 5.5 beta ships with the snazzy-looking new Bento skin, which is somewhat spoiled by the “Winamp Bento v0.7” and “Winamp 5.5 BETA” text in the top-right and bottom-right corners. Fortunately, these can removed fairly easily.
In the skin folder (C:\Program Files\Winamp\Skins\Winamp Bento\xml), open player-normal.xml in a text editor and remove or edit the line beginning text id=”reporter” (line 78 in Beta Preview 1). This will allow you to edit or remove the “Winamp 5.5 BETA” text.
To do the same for the “Winamp Bento v0.7” text, open player-normal-group.xml and edit/remove the line beginning text id=”gen.infotxt”) (line 436).
Next time you load Winamp (or hit F5 if Winamp is already running), the text should be gone or replaced with your custom text.
This will probably invalidate any bug reports you give to Nullsoft, and obviously will not magically transform your beta copy into the final release version, but hey, it looks heaps better. :)