I need help to decrypt my HDD.
It was encrypted using BitLocker on Windows 7, now I am at work I need it urgently and I only have Windows Vista Business(x86, sp2).
If you have a removable drive formatted as FAT, FAT32, or exFAT you may be able to use BitLocker To Go, which can be downloaded from BitLocker To Go Reader
In addition, as per comment by ramhound:
All versions of Windows after Windows 7 have the capability to read a
Bitlocker protected device.
The FAT limitation of Bitlocker to Go was also removed as the
program itself became a feature of Windows.
BitLocker Drive Encryption Overview
What happens if I try to open a BitLocker-protected, NTFS-formatted removable drive by using a computer running Windows XP or Windows
In most cases, Windows XP and Windows Vista will not be able to
recognize a BitLocker-protected, NTFS-formatted removable drive. In
many situations, the user will be prompted to format the drive.
Because of this, it is recommended that removable drives be formatted
by using the FAT, FAT32, or exFAT file system when using BitLocker.
What is BitLocker To Go?
BitLocker To Go is BitLocker Drive Encryption on removable data
drives. This includes the encryption of USB flash drives, SD cards,
external hard disk drives, and other drives formatted by using the
NTFS, FAT16, FAT32, or exFAT file systems.
Can I save files to my BitLocker-protected removable drive when I am using Windows XP or Windows Vista?
No. The BitLocker To Go Reader provides read-only access to
BitLocker-protected removable drives.
Can I download a copy of the BitLocker To Go Reader?
Yes. To download the BitLocker To Go Reader, see Microsoft Download
Center: BitLocker To Go Reader.
Why am I unable to access my removable drive on computers running Windows XP or Windows Vista when using the BitLocker To Go Reader?
The most common reason for this situation is that the drive is not
formatted by using the FAT, FAT32, or exFAT file systems. To check for
this, insert the drive in a computer running Windows 7 or later,
right-click the drive, and then click Properties to see the file
format of the drive. Another reason could be that the system
administrator has disabled access to removable drives from previous
versions of Windows by using the BitLocker Group Policy settings. To
check for this, attempt to access the drive from a computer running
Windows XP or Windows Vista that is not joined to the domain.
Source BitLocker Frequently Asked Questions (FAQ)