Combining hard drives

It would depend on what other hardware you have. Putting them into a RAID 0 (assuming you want space) will require wiping both drives.
Depending on the version of windows you have, you could create a software striped volume (still wipes the disks).
 

Yes, You can - RAID 0 or RAID1
Use onboard RAID or add a PCIe card, if a card is used, look for a card the offer at least x2 lanes V2 (5Gb per lane)