I would recommend ConvertX2DVD .Its a commercial-ware the free version has a watermark feature i think . But its worth the cost . Its the best DVD authoring software i have used (i have tried others like Nero Vision , Sony DVD studio etc etc) .
The following are its standout features
> Can handle any format including .mkv
> It can pack in 6 movies into a standard DVD without significant lose of quality .
> Very simple interface . Shallow learning curve .
> A number of menu theme options including those with the ability to upload your own audio file .
>A simple pdf manual from which you can quickly learn to use it effectively .
With this nifty software i can design a professional movie DVD within 4 minutes . The conversion may take a couple of hours (this is so in all softwares)
PS : didnt notice the 'freeware' requirement . anyways if you are not happy with freewares you should get CX2D