GoPro Hero 3 movie editing

Am having trouble with GoPro file recognition by Sony Vegas for editing. I could use the GoPro software but am told I need to install Quicktime to do so (have read that this is not now supported and could be "dodgy").
Have resorted to Windows Movie Maker, which recognises (and edits) the GoPro video but the play back is a little jerky at times.
I would really like to use my Vegas editor to do the job but can't find a converter that does the job.
I feel that the jerkiness is not due to my gear (Acer 5742Z) as has been suggested elsewhere ??

Thanks TZ. Quicktime gets very bad press nowadays, we are urged to delete it and find an alternative.
Have found a post which recommends VidoeLan instead, have searched the site and all I can find is VLC, which, as good as it has always been, doesn't solve the problem.

Just installed Qt lite as advised elsewhere.
Ran a 680mb Hero 3 video in Brorsoft (trial version) to test if this was the solution to my problems!
Video pre-view ran OK until towards the end then began to "stutter". Carried on with conversion to MPEG 2 anyway. This progressed to about two thirds of the file, then the machine shut down.
This had happened before with GoPro files, I am consequently no further on.
It would almost seem to me that my Acer 5742Z is not up to the job, I have checked Acer updates etc for anything I might need but am up to date, the machine has never shut down on me ever before.....Help