|Do you mean two drives on a single physical drive or two physical drives.|
If you mean two drives on a single physical disk then you are going to need some third party software like Partition Manager.
If you mean two physical drives the only way is to use RAID 0, sometimes called striping. RAID 0 is not recommended at all because of one drive fails you lose all your data with little chance of recovery.
You are far better keeping them as two single drives. With modern hardware there is absolutely no reason to be using RAID 0.