When I switched from VS2003 to VS2005, there were a few quirks that took some getting used to (and a few I am still adapting to). One of the biggest changes for me was the new web project structure. Thankfully, the VS team understood this, and we can get old-style web projects in the new IDE. Just download the tool from http://msdn.microsoft.com/asp.net/reference/infrastructure/wap/default.aspx
One caveat, this will not work in Visual Web Developer Express Edition.