I'm using disk management utility in windows 7. To extend one of my partitions. But I got this warning saying that I won't be able to start installed operating systems from any volume in the disk. What will I do with this? If I want to install some os on the space that will be left after extending the partition.

Details:
I plan to install the ubuntu 10.04, Linux Mint, and XP on the external drive, which I'm referring to at the top. It has 160Gb unallocated space. And I want to use only 60gb for the installation of those 3 os'. So I'm gonna extend the one of the partitions in the external drive by 100gb. But then I get the warning above. There's currently no other os on the external drive. And I plan to multi-boot the three os mentioned above using the external drive.