The only thing you need to know is do you have one or two hard drives currently.....you can only have four IDE drives and if you have a DVD player and a Burner plus one hard drive your ok...if you have two HD's then you'll either have to lose one of them or one of the disc drives.
Some old machines have an HDD upper limit (I had a Dell Pentium machine which would not recognise any more than 8 GB). If yours is pretty modern it will be OK or you can sometimes flash the BIOS to overcome hard disk recognition problems. sft42 is quite right as to the number of IDE devices your mainboard will handle (usually 4: as 2 per 2 IDE channels).