I've recently discovered the NTFS-3G/MacFuse plugin that allows you to both read and write to NTFS disks. This was a great joy, as I was able to use it along with this hint to resize and restore a big windows partition.
However, as others have found, it is not possible to select your NTFS Windows partition as a startup disk. One workaround is to simply make the partition non-writable, as described in this hint, but that defeats the purpose.
Below is an AppleScript cobbled together from bits and pieces on the internet that works around the problem. Note that you have to change the first two lines to match your system.
The first item, Untitiled has to be the name of the NTFS disk as it appears on your desktop. The second item is the firmware address of the disk. To find this, open a terminal window and type diskutil list, then press Return. For me, this gives:
/dev/disk0
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *298.1 Gi disk0
1: EFI 200.0 Mi disk0s1
2: Apple_HFS Macintosh HD 216.9 Gi disk0s2
3: Microsoft Basic Data 216.9 Gi disk0s3Mac OS X Hints
http://hints.macworld.com/article.php?story=20080116093511246