Ubuntu probably formatted it in an ext2 format (or ext3/ext4 which are based on ext2), which is not handled directly by Windows. There are free drivers for windows that will let you read, but not write, to an ext2-based file system.
rubberman
Posting Virtuoso
1,562 posts since Mar 2010
Reputation Points: 277
Solved Threads: 179
FWIW, you CAN create NTFS or FAT file systems on discs with Linux, which ARE directly accessible by Windows, including for write access.
rubberman
Posting Virtuoso
1,562 posts since Mar 2010
Reputation Points: 277
Solved Threads: 179
Does it appear in Disk Management?
Control Panel -> Administrative Tools -> Computer Management -> Click on Disk Management on the left hand side
Serunson
Posting Maven
2,578 posts since Mar 2007
Reputation Points: 533
Solved Threads: 46