It's best to configure wireless security using a PC connected directly to the router with a LAN cable, rather than over the wireless connection itself.
I'd recommend working through the following steps. After each step, make sure that all of the PCs that you want to use on your network are still working - if not then retrace your steps!
1) Change the Built-In Password
By default you gain administrator rights to your router by logging on as user "admin" using password "password". Not particularly secure, as everyone that has read a NETGEAR manual knows this! So change this default pasword - see Page 61 in the DG834GT manual
2) Change the wireless network name (SSID)
By default a DG834GT will always run a network named "NETGEAR". Again you should change this to something that the hacker trying to get into your network will not know or be able to guess. See pages 49 and 50.
3) Enable WPA-PSK Security Encryption
By default traffic between your wireless PCs and the router is sent in clear. Encrypt it using WPA-PSK, which is a stronger encryption protocol than WEP. Instructions to set it up are on Page 60.
4) Disable broadcasting of the wireless network name (SSID)
Having changed the network name earlier, prevent your router from broadcasting it for other stations to discover. Instructions on page 51
5) Restrict wireless access using the Wireless Station Access List
Once you are sure that all of your wireless PCs can access your secured network, lock down the access list so that no new PCs can be connected (even if they are correctly configured with all of the above). Covered on page 55.
Well these are my suggestions - ready to be shot down by others that may disagree
!!
RC