Also, take a look at this thread. Wireless security is addressed and it's pretty interesting. There's some good resources offered, so I'd recommend taking a look at them.
If you really want your wireless network secure, you're going to have to know what you're doing. There are far too many people who use it as an easy alternative and leave themselves wide open and enver know it. At least you've been smart enough to be watching.
It looks like you'll want to take some extra steps beyond just setting up the WEP key.
Security is always a trade-off with convenience. If you want to make it secure, take the time to learn and do it.