when you did that /mbr thing, you overwrote your master boot record with a microsoft boot record. this boot record just contains the info for how to load windows off yr first hard drive. If you want to get into linux, you can either reinstall it, setting up lilo to have both OSs as choices to boot from, or if you don't want to reinstall linux, you will need a linux rescue disk. since i have never needed one, i am not the best person to tell you about them, but i gather they are fairly simple to use.
Somebody who has used a linux rescue disk will probably fill you in....