Since somebodies asking about a portable Visual Basic, what about a portable C/C++ compiler. DevC++ from www.bloodshed.net is one of the best free C/C++ IDE package. And it's not that hard to make DevC++ into a portable package.
For ease, I put it in a NSIS package which unpacks the compiler, run its, and then waits for it to close so the files can be remove. Works perfectly, all I have to do now is make the NSIS package load registry settings from a file, and when the compiler closes, hopefully save any changed registry settings for DevC++ back to that file.
The IDE is opensource, so there's not reason it can't be edited to load/save it's settings from a file, or that a portable version similar to the one I'm currently using can be made.