Today I ran into more issue when working with deployment of my very first Web Part using Visual Studio 2008 on a 64bit Windows 2008 OS. One important tip when trying to deploy using a SharePoint WebPart for within Visual Studio as that you MUST add the VSeWSS user to the Sit Collections Administrators list. By default that will be just the Primary and Secondary admins of the Site Collection.
Note that you will probably only run into this issue if you have installed Visual Studio 2008 extensions for Windows SharePoint Services 3.0, v1.3 WITHOUT first creating the VSeWSS Application Pool. Please refer to the Release Notes as it will explain how to add the VSeWSS local user to all the required groups.
CAUTION: if you come across a post on the web that tells you to run this comment, then be VERY CAREFULL as it will knock-out your 64bit WSS SharePoint Web Applications if that's what you have: cscript %SystemDrive%\inetpub\AdminScripts\adsutil.vbs set w3svc/AppPools/Enable32bitAppOnWin64 1. Only Enable 32-bit on the VSeWSS App Pool.
Hope you have as much fun as I did, but it is great when I was finally able to deploy from within Visual Studio.