You can use fsinfo to check it.
Results below show that D: drive has 4096 which is default.
For SQL server databases Microsoft recommends a block size of 8K and up.

fsutil fsinfo ntfsinfo f

c:\>fsutil fsinfo ntfsinfo d:
NTFS Volume Serial Number :       0x60f2135af213342e
Version :                         3.1
Number Sectors :                  0x000000000237efff
Total Clusters :                  0x000000000046fdff
Free Clusters  :                  0x000000000046bcfa
Total Reserved :                  0x0000000000000000
Bytes Per Sector  :               512
Bytes Per Cluster :               4096
Bytes Per FileRecord Segment    : 1024
Clusters Per FileRecord Segment : 0
Mft Valid Data Length :           0x0000000000008000
Mft Start Lcn  :                  0x00000000000c0000
Mft2 Start Lcn :                  0x0000000000237eff
Mft Zone Start :                  0x00000000000c0000
Mft Zone End   :                  0x000000000014dfc0

It is highly recommended that all partitions are configured by using the DISKPAR (Windows 2000) or DISKPART (Windows 2003) commands.
When using DISKPAR, adjust the alignment by 512 bytes, and when using DISKPART, the disk should be aligned to 64.
The reason for this is due to the original master boot record design of WinTel based systems.
The master boot record for all drives is 63 blocks (1 block = 512 bytes).

Description of DISKPART commands: http://support.microsoft.com/kb/300415

The physical disks want to read and write data in 64 block chunks.
Because the master boot record is only 63 blocks, this puts the first block of actual data in block location 64, where it should be in block location 65.
That forces the disk to read 128 blocks for each 64 blocks read to the disk, thereby increasing the work needed to be done and decreasing performance.

Once a partition has been created without the alignment offset, there is no easy way to change the offset.
The only method for doing that is to create a new volume and partition with the offset, take down the SQL Server and manually migrate the files to the new drive in an offline manor.

Microsoft is including this procedure as the standard when creating partitions starting in Microsoft Windows 2008 Server.

Disk Partition Alignment Best Practices for SQL Server 2008
http://msdn.microsoft.com/en-us/library/dd758814.aspx