MSDE and Exchange on same NT Server

I am installing MSDE on a NT4 server (for Great Plains software) and am having issues. I have repeatedly stopped and restarted server services, and made sure file and print services are enabled. SYSTEM has full control over the directory I am installing. Exchange is on the server. Drive C is 1.87 free and drive R is 12 gig free. I want to install on drive R. It will not let me install on Drive R -- only C. This is an easy install, should take 15 minutes but I have been fighting with it for several hours. The only 'unknown' issue is whether or not Microsoft Exchange and MSDE on the same server could be the culprit. Any ideas? Best regards Stephanie

Is R drive a Physical drive? or a mapped drive?

I dont think you can install it on a mapped drive.