They'll be fine as long as you don't try to RAID.
Probably won't simply work. Most of the time you need identical drives, though some controllers let you use different models and even different capacities (in which case only that of the smallest drive will be utilized)Ok, and what if i try to?
I currently have a "320Gb samsung SATA2 16MB 7200RPM"
I'm going to buy another HDD: Samsung SpinPoint F1 750GB SATA2 32MB 7200RPM
Will they work together or will I face problems?