As you can see from Figure 2, basic wireless setup for the GS5 is essentially the same as for the WET54G (the GS5 even has the same default IP address of 192.168.1.226). So click on over to that review if you need the details and I'll just cover the differences here.
Figure 2: Setup screen
(click on the image for a larger view)
The main difference I found from the original WET54G is that the GS5 supports both 802.1x authentication and WPA-PSK and WPA RADIUS (aka "Enterprise") mode in addition to 64 and 128 bit WEP. (From perusing Linksys' download page, I found that the newer WET54GV2 has firmware that supports WPA, but the original WET54G doesn't.)
The GS5's 802.1x authentication settings let you enter a RADIUS server IP address, RADIUS port number, pre-shared key and re-authentication timeout. There's even a View Log button that shows the results of the authentication process.
Figure 3: Security settings
Figure 3 shows the Security screen with RADIUS EAP authentication selected. You can also choose MD5 and TTLS EAP methods and the screen will change to present the proper entries for you to fill in. Of special note is that the GS5 supports WPA only in Infrastructure mode. WEP 64 / 128 will have to suffice if you use it in Ad Hoc mode.