The most logical place to check woul be in your project settlings, when you first opened your project.
You set it up to capture as an AVI -- but it sounds like it might be an uncompressed AVI. (Assuming you're capturing from a DV camcorder) it should be set to NTSC-DV/AVI (or PAL-DV if you're using the PAL system).
As DV compression is about 5 to 1, that would account for the increased file size.
I recall it was originally set for the 'NTSC DV' template - which has 'lower field first' as a 'field order' setting. I had gone in and changed 'field order' from the default of 'lower field first' to 'upper field first' - as I am capturing from an analog camcorder through a video capture card. I had hoped this was going to change all of my captures to 'upper field first' - but it did not. I still have to manually change their properties in the media pool of each project.
I tried resetting the template to 'NTSC DV' and the file size remained the same - 1 GB per minute of video.
The issue is apparently with your capture settings rather than the project settigns for MovieStudio (which have no effect on your capture size, since this project isn't doing the capture, of course).
Check to see if your capture software (since your'e capturing analog) can be set to AVI/MJPEG. This should give you the best compression with the least loss of quality.