By looking for a VB.NET option on Linux, I presume that your primary
motivation is to get to use a tool which is very simple to pick up on.
There is a VB clone called Gambas:
http://gambas.sourceforge.net/
Lazarus is a Delphi clone.
http://www.lazarus.freepascal.org/
If you insist on using a .NET type of tool, then look at developing on the
Mono framework.
http://www.mono-project.com/Main_Page
One good option is to also consider Java as a development platform. Use
Netbeans 6 and the Matisse GUI Builder and you can create neat user
interfaces quite easily and also be able to run it on multiple platforms.
(Personally, this would be my choice)
Alternatively, you can look at PyGTK.
Other options include WxWidgets.
http://www.wxwidgets.org/
Regards,
PK