VS 2008 can target both the 2.0 and the 3.0 (as well as the new 3.5) versions of .NET. But if you're not using 3.5, why would you want to use VS 2008?
the horse's Scott Guthrie's mouth:
- Nested ASP.NET master page support at design-time
- Rich CSS editing and layout support within the WYSIWYG designer
- Split-view designer support for having both source and design views open on a page at the same time
- A much faster ASP.NET page designer - with dramatic perf improvements in view-switches between source/design mode
- Automated .SQL script generation and hosting deployment support for databases on remote servers
I for one am looking forward to it.