Simplest way to convert 1080p h264 mkv to 720p mkv?

[aer]

I have an .mkv file with the following properties:

Video: MPEG4 Video (H264) 1920x800 23.98fps [Video]
Audio: DTS 48000Hz 6ch [Audio]
Text [Subtitle]

I want to convert the file to a format that my computer can handle. I know it can handle 720p mkv files. I'm not too concerned about maximizing quality. I am just looking for a simple process that will (1) prevent audio sync problems and (2) preserve mkv-style subtitles.

I downloaded MeGUI at the recommendation of a forum post I found via google, but I can't figure out how to configure it. Can someone please recommend the settings I should use? Or maybe there's a way to do what I want to do? Also, how long would it take for a 1.8ghz dual core processor to convert a 10GB 1080P h264 mkv file? Thanks in advance for any help.

[Baldrick]

Uncropmkv.