This will cover making a Single Layer ISO on your Hard Drive.
Firstly make sure your Vob, Ifo and Bup files are in a folder called VIDEO_TS
Next, open ImgBurn in Build Mode (Click 'Mode' -> 'Build') and switch the Output Mode to Image File (Click 'Output' -> 'Image File').
Click the 'Browse for a folder...' button in the source box, and navigate to the folder where you saved the files.
When you have chosen the folder you require you can use the Calculator