They will charge a fee to become a member since the business that run these websites have to pay to have access to the video games and keep their sites. The costs are small - normally about $35-$45 - and provide you limitless downloads whenever you desire. The download costs are fast, the files constantly work and it is totally legal - making it a much better option than "complimentary" sites. The membership will include the software application you require to be able to transfer files onto your PSP.
If your PSP firmware is not version 1.50, you can downgrade the firmware but do be warned it will void your PSP service warranty and there is an opportunity when downgrading, it will download app damage your PSP.