I got this same message after using Disk Utilities to create a new partition formatted in FAT 32, booting from my windows XP CD, reformatting that partition to NTFS, and installing Windows XP on that partition. (So I can dual-boot without using Boot Camp Beta, which is expired)
I worked around it just fine by holding the "alt" key when booting, which (after entering my firmware password) allows me to select the boot partition. It's like I somehow selected "Neither" for my default startup disk.
It's possible that your problem goes beyond this.
By the way, in my Windows reformat, I did end up deleting several 200 MB partitions that appeared on my drive...it looked like this:
(partition) (size) (name) (file format)
Partition 1: 198 MB [unknown empty
Partition 2: 250000 MB [Windows FAT32
Partition 3: 202 MB [unknown empty
partition 4: 850000 MB [Unknown unknown
this one is formatted in the mac file system, but XP (of course) doesn't
recognize it....
partition 5: 201 MB [unknown empty
Anybody know what's going on here? I sucessfully merged the first three from the XP cd, but I don't know what's up with Disk Utility and why it leaves these spaces after partitioning.....