RS or RX? If it's an RS then perhaps you should search for info on a Legacy instead of a Liberty.

If you have a understanding of how your engine works it might be ok, try and search for a workshop manual for your car on the internet or just buy one from the shops.
Are you mechanically minded and do you do any other servicing on your car because the timing belt isn't something you just a give a go at, the engine has four cams and once the old timing belt is off one of the cam lubes might be under tension and will want to move which can damage your valves.

So if you feel your confident to do the timing belt maybe get a mate to help you, if your not don't try it because a incorrectly fitted timing belt will stuff your whole engine and you will be looking at a $3000 rebuild.