I'm not familiar with Project Server but I am familiar with SharePoint. Web Parts in SharePoint can contain any arbitrary code and are more or less identical to regular ASP.NET web parts - in fact SharePoint web parts inherit from ASP.NET web parts.
From the second article you mentioned, it looks like Project Server contains its own set of SharePoint web parts, so you are likely to get better integration with SharePoint using these than simply by displaying a web page inside another one (sounds to me more like an IFRAME).
As a quick SharePoint overview, there are 3 versions of SPT 2007 - Windows SharePoint Services 3.0, which ships alongside Windows Server 2003; Microsoft Office SharePoint Server (MOSS) 2007 Standard, which adds portal, content management and enterprise search features; and MOSS 2007 Enterprise, which adds other tools for line-of-business app integration, including the Business Data Catalog (BDC). The BDC is meant to be an easy way of getting line-of-business data into SharePoint. It uses an XML definition file but don't try cutting one by hand!
However, SharePoint 2010 has now been released (I'm not an expert). SharePoint 2010 Foundation is roughly equivalent to WSS 3.0. SharePoint 2010 is 64 bit only. It looks like quite a nice step up from WSS 3 / MOSS 2007. Don't forget though that SPT 2007 is already 3 years old, so it's already well advanced down its support lifecycle.