Windows 7: Burn blu ray videos w/o blu ray burner

Is it possible to burn blu ray video without a blu ray burner? I've also heard that you can convert it to other types like dvd and burn it. But would it affect/effect the result quality?

Umm, yes, kind of...
Blu-ray isn't a codec as such, it's a media format much like floppy disks, cd-r's & dvd-r's.
Advantages of the Blu-Ray format include larger storage capacity, which allows for higher resolutions (HD), longer play times, and less lossy compression methods to be used.
This means that because Blu-Ray video doesn't necessarily have to have come from a Blu-Ray disc, it is possible to encode or copy Blu-Ray video to your pc without copying it directly from a Blu-Ray player.

As it's also possible to convert from the various codecs used with the Blu-Ray format to other video codecs, yes, you can then transfer them to other removable media formats including dvd's. You just need the right conversion software to do the job.

Will it affect the quality of the resultant converted file? That depends on the codecs that you use to convert the file to and the settings that you use. These variables will most likely be determined by the size limitations of the removable media that you intend to copy or burn the end result to.

*Disclaimer*
This response is intended to be informative only, and in no way condones piracy. Check your local laws before attempting to duplicate any materials that are subject to copyright. Please don't ask me how to bypass encryption methods or make pirate copies of anything, my response WILL offend you.

Thanks Orpheous! That helped me a lot.

You're welcome
If after all that you're still interested in video conversion, try AlltoAvi or Handbrake, AlltoAvi is probably the easiest to start with. They both have user based support networks that can help you out with settings etc.
Be prepared to be frustrated with failed attempts, but the end results are worth it if you're keen.
Good luck!

blueray discs cannot be read or written with a DVD writer, becausee wavelength of laser is not same. So it is not only a "software" difference.

Now of couirse you can convert from one format to the other (if you have a reader compatible), but you cannot transform 25GB (or 50GB) into a 4.7GB (or 9) without loss of quality, obviously.