I wanted to post a couple tips relating to some issues we've seen with this scenario, mostly because I did some searching of my own and there's not a lot of guidance out there (yet).
Issue 1: Installing and Configuring Windows SharePoint Services on LHS
We've been doing this via automated testing for some time, but only recently discovered that doing it manually is actually a bit tricky. Installing and configuring WSS via the LHS component manager is pretty straightforward; but we discovered that manually creating a web application (or modifying an existing one) via the SharePoint admin website fails (with an Access Denied error page).
You can work around this by using stsadm.exe - from an elevated command prompt. You might be able to avoid this by disabling UAC, but I do NOT recommend doing so.
Issue 2: Manually installing IIS on the TFS Application Tier (as a prerequisite for installing SQL Reporting Services)
I did this by hand recently, after stumbling through a problem where the SQL installer kept claiming IIS was not installed, even though it was. It turns out that the default IIS install options do not include a feature that the SQL installer needs - HTTP redirection. Not having it causes the installer to flag as if IIS was missing entirely.
These issues will almost certainly be addressed in due time - Server 2008 is still pre-release software, after all. But, if you're trying to evaluate TFS Orcas Beta 2 (aka Microsoft Visual Studio Team Foundation Server 2008 Beta 2), hopefully this will help you succeed.
Everything will come around in time.