I would like to know if it's possible to move the files on a given partition to the begin of the disk, where the read/writes are faster.
I currently have Windows Vista installed on the first partition of the disk with a few more partitions for work related files and other stuff.
Would this guarantee that the OS partition (which was the first to be created) is located at the begin of the disk?
Would a defrag program help with this or the various partitions limit the location of the files on the disk?
No, it's not possible. Physical partitions separate a disk into circular regions. The first partition occupies the outer ring of the disk, and the next partition occupies the ring inside that one. You can move files within a partition, but all the files of one partition come before any files of any other partition.
If partitions were wedge-shaped, then what you request would be possible.