There's an application called BitLocker to Go for XP that will let you read BitLocker encrypted drives. (Download Here)

However, one major caveat is if the drive is formatted with NTFS (common), then you will not be able to read it on XP. The drive must be formatted with FAT32/exFAT for it to work in XP. XP needs a windows update to read exFAT. (Download Here) FAT32 is limited at 4GB file sizes. exFAT is much better.