Rhut roe, Raggie. You just checked in a merge operation affecting 100's of files in TFS against the wrong branch. Ooops. Well, you can simply roll it back, right? Select the folder in Source Control Explorer and...hey, where's the Rollback? 
Executing the TFPT rollback command (with the /changeset option in this example), will earn you a prompt to get the latest. Go ahead and click Yes. 
Next, you'll be presented with all the assets (files) in that folder involved in that particular changeset (228 in this case). We only want to roll back Program.cs so we'll only select that file. If you Ctrl-A and uncheck one box, it will uncheck them all. Click Rollback.
Rollback isn't supported in TFS natively. However, it is supported within the Power Tools leveraging the command-line TFPT.exe utility. It's fairly straightforward to revert back to a previous version--with one caveot.
First, download and install the Team Foundation Power Tools 2008 on your workstation. Before proceeding, let's create a workspace dedicated to the rollback. To "true up" the workspace, the rollback operation will peform a Get Latest for every file in your current workspace. This can consume hours (and many GB) with a broad workspace mapping. To work around this, I create a temporary workspace targeted at just the area of source I need to roll back. So let's drill down on our scenario...
I'm working on Program.cs and I accidentally check in a change I shouldn't have. Oops.
Let's create a workspace mapped just to the folder housing Program.cs so we avoid a massive, entire workspace "Get" during the rollback operation. 
Afterwards, select that workspace and perform a Get Latest (just to establish the file system directory). Open up a Visual Studio 2008 command prompt and browse to the workspace on the file system.
To perform a rollback, you can target a changeset or a filespec. I prefer the specificity of the changeset but whatever works for you. You also have flexibility with merge and recursive behavior. Here's the full write-up on MSDN for Rollback. Alternatively, just type in a
TFPT rollback /?
Executing the TFPT rollback command (with the /changeset option in this example), will earn you a prompt to get the latest. Go ahead and click Yes. 
Important to note here with the changeset option: you want to identify the changeset one prior to the version you wish to rollback to. So, if I want to rollback to changetset 227, I want to use changeset 228 in the TFPT operation.
Next, you'll be presented with all the assets (files) in that folder involved in that particular changeset (228 in this case). We only want to roll back Program.cs so we'll only select that file. If you Ctrl-A and uncheck one box, it will uncheck them all. Click Rollback.
Next, you'll receive feedback at the command line about the operation. But wait, you're not finished! Rollback is a local operation. You still need to check in your change. This is a great "safety" if you messed up the rollback itself. Just Undo Pending Changes.
Ok, so we're ready to check in our changes. 
Looking at View History once more, note we actually have a third version and changeset now: 229. But, we've indeed returned to the original (the first, changeset 227) version of the source.
Being back to square one never felt so good...
Comments
Check out; get a specific version of the branch that you want to roll back, undoing local changes when prompted. This checks it all in to the version to which you rolled back.
I thought the instructions he had were longer and more confusing than just doing it the original way.
6
5
was not my project (4)
3
2
1
and I realize that I need to roll back to 2.
Do I issue tfpt rollback /changeset:3 or do issue individual commands (one for each of my changeset numbers (6, 5, 3)?