WEP (Wireless Encryption Protocol) only encrypts local communications through your router. So, you should evaluate whether or not it's really necessary. Chances are, unless you live in an apartment complex or something like that, you don't need WEP. The structure of most houses will likely keep the rather weak radio signal inside.
WPA is the same thing... It's basically a different form of encryption designed to address some of the flaws with WEP. However, unless there's the possibility of someone nearby with a wireless system piggybacking onto your little LAN (like in an apartment complex or college dorm), it's not necessary. Communications between your router and the Internet are still going to be unencrypted, it's just communications to and from your computers and router that will be encrypted.
Simply turning off SSID broadcasting on the router will stop probably 99% of all people who would want on your network anyway. Those that could get around that are also likely the type who will be able to crack WEP/WPA encryption, given enough time.
So, you might want to first evaluate whether or not you really need WEP/WPA.
I had previosly set up a wireless home network between my two xp machines, at the time the level of encryption was set to 64 bit however i have since increased it to 128 bit wep....how do i change the keys in the network area so the two machines can still be 'networked' through the router..ps they can access the internet fine but they just dont 'see' each other since the security update. Also could someone explain to me what wpa is? is it better than the level of encryption i currently have on? is 128 bit wep enough so that i can leave my router on and plugged in to the net 24/7 ?