What's WEP?
If you have a router modem that came with the internet provider, it may be on the label. I assume your sistor won't tell you what it is.
Under Settings all the way down is Network and under Status list it says that the connection method is Wired but there are not options there.
If 'wired' is selected already, may be the easiest way is to get a Cat5 cable that is long enough to reach your router. You can bring the PS3 to the router too but then you need to hook it up to a monitor in that location (hopeful you have a small one nearby) so you can see what is happening. Using the wired method you do not need the 'wep' key.
If you don't want to buy a long cable and cannot borrow one, then follow Mr. Garcia's link and go the USB route. I assume you do have a USB flash drive right? To use USB or any other storage media, be sure to select 'system update (the first one under 'setting') and then select Update via Storage Media.