hindi naman problema yan whether its 2.5" (for laptops) or 3.5" (for desktop) same lang naman gamit na connection (mostly SATA), so pwede parin isaksak sa SATA port ng desktop motherboard mo yan. ang isang magiging possible problem mo lang dyan is kung saan ilalagay in case gusto mong gamitin as HDD for desktop (some cases merong case ang 2.5" so you can put it in the 3.5" bay sa casing
kung ayaw mo magbukas ng casing, you can also use 2.5" external casing para via USB ang connection sa PC mo