Exchange drive loses space weekly

Running Exchange 2000. Approximately every 7 – 10 days I lose all of my space on the drive where exchange resides. Oddly, I can’t find where the space goes. For example, I usually have nearly 7.5 gb free. Then, I find only 400MB free and the Exchange service stops dead. Need some ideas on where to look. This has become an annoying issue since it started approximately two months ago. Is this some sort of mail database issue?