Well I have always been using two operating systems ( WinXP and Linux Fedora ) on my desktop. I have always been of an opinion that dual boot might not be a healthy option for your HDD. So this is what I did to encounter this problem.
I managed an extra Hard drive of decent capacity ( 10 GB in my case ) and this was targetted for installing Linux. I kept both drives as Master, one as primary and other as secondary. Whenever I need to switch the OS, just get into the BIOS while booting and select the appropriate HARD DISK (not the logical volume).