Video Editing Program that lets you edit from 720p MKV / MP4

[TheRandomOne]

Are there any programs like this out there for XP ? I have Adobe Premiere but it does not let me edit straight from these files

[hello_hello]

It depends a little on your definition of editing. MKVMergeGUI will split and append MKVs so you can use it for basic cutting. Video To Video converter can do a similar thing and it has a preview (there's a couple of editors under the Tools menu).
Alternatively, if you open an MKV using Video To Video Converter and select "direct stream copy" from the list of conversion presets, you could probably remux the video into a Premiere friendly format without needing to re-encode it to do so. Depending on the type of video and audio within (whether the output container supports it), you could open an MKV, use "direct stream copy", and set the output container to MP4 (for example).