If you're a student, then Microsoft has just announced a new program called DreamSpark to get Visual Studio 2008 Professional Edition (and Expression Studio and Windows Server 2003 and XNA Game Studio and SQL Server 2005) for free.
As Aaron points out, once you've got Visual Studio you can download the VS SDK (also for free) and start extending it.
If there are any academics reading my blog (I'm hoping that some of my academic colleagues might take a peek now and again), please let your students know about this.
Putting on my Lecturer's hat, I'd encourage all Computer Science students to try out both Visual Studio and Eclipse before they leave college, as it's very likely that a potential employer will be using one or other, and sometimes both. Also, the more experience you have with different development environments and programming languages the more transferrable and rounded your computing skills are likely to be.