Is WEP used in conjunction with a wireless access list adequate security?

No.

WEP is trivial to break. MAC addresses aren't secure. They can be trivially spoofed. Take a look at The six dumbest ways to secure a wireless LAN:

MAC filtering: This is like handing a security guard a pad of paper with a list of names. Then when someone comes up to the door and wants entry, the security guard looks at the person's name tag and compares it to his list of names and determines whether to open the door or not.

WEP is easy to crack (there are videos of it being done in 10 mins, etc) and MAC addresses can be spoofed. However, what are you 'securing'? If this is a business then NO, this is definitely not enough security. If it's your home internet, and your 10 neighbors all leave their wireless open, and you have a software firewall on your computer, then maybe this is enough.

It's like when I go hiking in the woods with my girlfriend. I'm not scared of the bears... I might not be able to outrun them, but I can at least outrun her!

No WEP is not adequate security. Mac addresses are sent as part of the wireless packet and therefore easy to intercept and spoof.

If you need to use WEP you need to install a 3 NAT router setup as shown below. NAT router 1 (NR1) is connected to the internet on the WAN port. NAT router 2 (NR2) WAN port is connected to NR1 LAN port. NAT router 3 (NR3) WAN port is connected to NR1 LAN port.

                       ----------NR2--------------Wireless WEP Unsecure 
                       |
Internet  ----- NR1----|
                       |
                       |
                       ----------NR3--------------Wireless WPA Secure

This will allow the WEP access to get to the internet. The NR3 router would block access to your secure network. One other advantage would be to allow guest access to NR2. That would allow Internet access without providing access to your local secure network.