I use Adobe premiere pro CS5 and for the most Canon 5DmkII (mov). In Premiere Digital DSLR - 1080P25.
And I use Sony HDV1080i25. Is this ok to put HDV (m2t) inside Digital Dslr timeline? In timeline I got a yellow line over mov file and over m2t files i got red line and it takes time to confirming.

Sometimes i use som mov file from Canon G9. But thay are only 640x480. So how can I get this bigger?

(Have a Intel i7-920 with 12GB ram).

There is nothing inherently wrong with intercutting HDV and DSLR footage on the same timeline. For best results they should be the same framerate. Shooting the HDV in progressive mode if that is an option may help it match the DSLR footage better.
The SD footage can be intercut if you want. There are a variety of methods for converting it to match the HD sources, but none of them are going to change the obvious fact that it was originally shot at lower resolution. CS5 is nice in that it will allow you to edit the SD files without converting them, and get reasonably decent results, so you should be able to just drop your SD sourccefiles into your HD timeline. (You may want to make sure you are set to "scale media to framesize" by default to save you some extra work)

Scale media to framesize helped. I only got some black field on each side. But the Audio goes to Audio 4 in timeline? Why and why cant i move it to Audio 1 or 2?

What is best to export? I have a WDTW live who take 1920x1080P. I export to a externial harddrive. H.264 blue-ray or just H.264? H.264 Preset HDTV 1080P 25 then i got ia mp4. Is this the best quality i can get. Is this the same quality as my orgioal Canon 5DmkII mov file?

And some times to DVD 4.5GB? Mpeg2-DVD?

Mono sound can only go into a mono track, stereo only in a stereo track. Default is three stereo tracks, do mono sound will end up in a newly created mono track.

I hope the external is an eSATA, not a USB drive.

H.264 is the best export codec, but the quality depends on the encode settings, bitrate, number of passes, etc. It will always be less quality than the original source material because of the long GOP nature. After editing it needs to be re-encoded, but it is the best you can do, apart from not editing such material.

For DVD, use MPEG2-DVD.