Important data such as your photos should always be backed up to at least 2 different places. I would suggest for long term storage burn the files to DVD media. The 2nd backup can be to a hard drive. You can use any number of backup software applications. Apple's Time Machine is included with your operating system - see the web page put together by Pondini- one of the high level people on these forums.
Bombich's Carbon Copy Cloner is an alternative. I have used it for a number of years and found it reliable.
Depending on the importance of your data you may also want to consider an offsite backup using a service such as Carbonite or CrashPlan. This protects your data against catastrophic failure such as complete hardware loss due to fire, flood or theft.
You can read up on NAS here.
Best of luck.