There is currently no way to do that from ViEmu. It can be done using the Visual Studio interface, by right clicking on a tab and selecting "new horizontal tab group". Unfortunately, at first inspection, there is no way to access this programmatically. This is pending more investigation. Also, a full emulation of vim's window model is very, very difficult in VS - VS has a very different understanding of windows/tabs/files/etc...
Thanks for the point about :u, I didn't even know that was a way to get undo too. I use 'u' for the same function (and ^R for redo, since ViEmu supports the full VS undo/redo queue).
File name completion is planned for a further release - I want to implement it in a nice way, so that it will work for all kinds of arguments (and not only for filenames), so it'll need some time yet.
Ctrl-V and block selections should work - the reason it probably doesn't is that Ctrl-V is mapped to "Paste". You can use Ctrl-Q as an alternative, or you can remove Ctrl-V's "Paste" mapping so that ViEmu will receive and process it. If you want to remove it such that toggling ViEmu on and off with Ctrl-Shift-Alt-V will dynamically restore/remove it, you can follow the following instructions:
1. Go to Tools|Options|ViEmu->Keyboard
2. Click the "Restore" button under the saved keybindings list (to restore the initial pre-scan state).
3. Click the "Forget" button under the saved keybindings list to make ViEmu clear the remembered list. After this, the list on the left should be empty, and the list on the right will probably show a lot of clashing keybindings.
4. Change the list of keys scanned to add/remove any one you don't like (for example, change from the default "RFBDUWTQEYOINP]" to "RFBDUWTQEYOINP]V" to add Ctrl+V to the combinations checked and thus remove the regular "Paste" binding from Ctrl+V, and leave it free to enter visual-block mode.
5. Click the "Apply" button (the list on the right should now show "Edit.Paste" as a clashing keybinding)
6. Click on the button "Save and Remove" under the current clashing keybindings list
Let me know if you have some problem with the process.
Thanks for the feedback,