The mdf and ldf extensions are extensions for primary data file and log file respectively by convention; they are not mandatory. So even if you did not rename your files there will be no issues. However, if you do want to rename them for consistency (which is a good idea), do what I suggested in your other question here: http://www.sqlteam.com/forums/topic.asp?TOPIC_ID=186994
You should follow that procedure exactly - don't simply rename the file without doing the other things. Also, test it in an environment before you do it for real.